Who else vividly remembers the joy of unwrapping a Little Debbie Cosmic Brownie? That perfect square of rich chocolatey goodness, topped with a shiny chocolate frosting and those unmistakable, vibrant rainbow chips – it was pure bliss! If you’re anything like me, the mere sight of rainbow chips on a dessert instantly makes it irresistible. These homemade cosmic brownie cookies capture that exact essence, delivering the rich, fudgy texture of your beloved brownie in a chewy, satisfying cookie. They offer all the nostalgic charm of the classic, but with the superior taste and texture that only a homemade creation can provide.

For this recipe, I’ve leveraged my absolute favorite chocolate cookie base. It’s the same reliable and delicious foundation used in my popular chocolate s’mores cookies and the incredibly simple one-bowl triple chocolate chunk cookies. This base guarantees a soft, chewy, and deeply chocolatey cookie every time. To truly mimic the cosmic brownie experience, I’ve generously topped these cookies with a simple yet decadent homemade chocolate ganache, finished with those essential, colorful rainbow chocolate chips. My quest to find these specific chips was quite an adventure – a true “journey,” as I’d put it! I eventually had to get them shipped to my hotel room during a trip to New York because they were nowhere to be found in London. Trust me, the effort was absolutely worth it for that authentic cosmic touch!

If you’re a true chocolate connoisseur and eager for more chocolatey delights, be sure to explore some of my other fantastic recipes. You might love my chocolate-dipped butter cookies, the delightful Nutella thumbprint cookies, the irresistible peanut butter Nutella cookies, the crowd-pleasing Oreo chocolate chip cookies, and the festive cocoa blossom cookies. Each offers a unique chocolate experience!

Why You’ll Adore This Cosmic Brownie Cookie Recipe!

• Effortlessly Easy – You don’t need a myriad of bowls or complicated techniques to whip up these cosmic brownie cookies. This recipe is designed for simplicity, requiring just two bowls – one for mixing the rich cookie dough and another for preparing the silky-smooth chocolate ganache. It’s perfect for bakers of all skill levels, ensuring a stress-free and enjoyable baking process.
• A Chocolate Lover’s Dream – If chocolate runs in your veins, then this recipe is an absolute must-try. These cookies deliver a double dose of chocolate with their intensely fudgy cookie base and a generous layer of luscious chocolate ganache on top. It’s an explosion of rich, deep chocolate flavor that will satisfy even the most discerning chocoholic.
• Luxuriously Rich & Fudgy Texture – Say goodbye to dry, crumbly cookies! These chocolate cookies are engineered for ultimate fudginess and a wonderfully rich, chewy texture. The careful balance of ingredients ensures they stay soft and moist, embodying the perfect brownie-like chewiness in every single bite.

Gather Your Key Ingredients

The success of these fudgy cosmic brownie cookies hinges on the quality and type of your ingredients. Here’s a closer look at what you’ll need and why:

• Cocoa Powder: For this recipe, I’ve specifically developed and tested it using Dutch-processed cocoa powder. This type of cocoa powder has been treated with an alkali to neutralize its acidity, resulting in a darker color and a smoother, less bitter chocolate flavor. Natural unsweetened cocoa powder, on the other hand, is acidic and reacts differently with baking soda and baking powder. Therefore, I strongly advise against swapping it out, as it could significantly alter the texture and rise of your cookies. Unsure if the cocoa powder in your pantry is Dutch-processed? Simply check the ingredients list! If it mentions ‘alkali,’ ‘processed with alkali,’ or ‘acidity regulators,’ then you’re good to go.
• Butter: I am always a proponent of using high-quality European butter for my baking. Why? European butter typically boasts a higher percentage of butterfat compared to its American counterparts (around 82% versus 80%). This higher fat content contributes to a noticeably creamier texture, richer flavor, and more tender crumb in whatever you bake. If European butter isn’t readily available, standard unsalted butter will work, but opt for a good quality brand. Ensure it’s at room temperature for optimal creaming.
• Chocolate: For the silky-smooth chocolate ganache, I highly recommend using semi-sweet or dark chocolate. The quality of your chocolate will directly impact the flavor and texture of your ganache, so choose a brand you enjoy eating on its own. You can use chocolate chips, but for the best melting consistency and ganache, finely chopped chocolate bars are often preferred.
• Rainbow Chips: These are the crucial element that gives these cookies their “cosmic” flair and nostalgic appeal! I used these particular rainbow chips, which closely resemble those found on the original cosmic brownies. However, if you find them hard to source (as I did!), don’t despair! You can easily swap them out for mini chocolate chips, colorful rainbow sprinkles (the nonpareil type works great!), or even other small candy-coated chocolate pieces for a similar effect.
• Heavy Cream: This is the essential liquid component for creating a rich and glossy ganache. You’ll need to use heavy cream, which is also known as double cream in the UK. Ensure it has a high fat content (typically 36% or more) for the best results; lower fat creams or milk will not create the proper ganache consistency.
• Eggs & Egg Yolk: Using both a whole egg and an extra egg yolk contributes to the fudginess and richness of the cookies, making them incredibly tender and chewy. Make sure they are at room temperature for better emulsification with the butter and sugar.
• Sugars (Granulated & Light Brown): The combination of granulated sugar for crispness at the edges and light brown sugar for moisture and chewiness is key to the perfect cookie texture. Brown sugar also adds a subtle caramel note.
• All-Purpose Flour: The structural backbone of the cookie. As with cocoa powder, precise measurement is important to avoid dry, cakey cookies.
• Baking Powder & Baking Soda: These are your leavening agents. They work together (especially with the acidic components of the brown sugar and eggs, balanced by the Dutch-processed cocoa) to give the cookies their perfect lift and chewy texture.
• Kosher Salt: Balances the sweetness and enhances the overall chocolate flavor. If using fine table salt, use half the amount specified.

Step 1: Cream the Butter and Sugars. In the bowl of your stand mixer fitted with the paddle attachment, or a large bowl with a hand mixer, combine the softened unsalted butter, granulated sugar, and light brown sugar. Beat on medium-high speed for about 2-3 minutes until the mixture is visibly light and fluffy, and has turned a slightly paler, almost creamy color. This aeration is crucial for a tender cookie. Add the vanilla extract, the large egg, and the extra egg yolk, then beat again on medium speed for another minute until everything is well combined and smooth, making sure to scrape down the sides of the bowl to ensure uniform mixing.

Step 2: Incorporate Dry Ingredients and Chill Dough. Stop the mixer and add all of your dry ingredients to the bowl: all-purpose flour, Dutch-processed cocoa powder, kosher salt, baking powder, and baking soda. Begin mixing on the lowest speed to prevent the dry ingredients from flying out of the bowl, gradually increasing the speed if needed. Mix only until the dry ingredients are just combined and no streaks of flour remain – overmixing can lead to tough cookies. Once combined, cover the cookie dough and chill it in the fridge for 30-60 minutes. This chilling step is vital as it helps the dough firm up, preventing the cookies from spreading too much during baking and resulting in a chewier texture.

Step 3: Preheat and Scoop. While your dough is chilling, preheat your oven to 350ºFahrenheit (175ºCelsius). Line two large baking sheets with parchment paper; this prevents sticking and aids in easy cleanup. Once the dough has chilled, scoop out generous portions – about 3 tablespoons each – using a cookie scoop or by hand. Roll them into smooth balls and place them onto the prepared baking sheets, ensuring adequate spacing between each cookie to allow for spreading.

Step 4: Bake and Cool. Bake the cookies in your preheated oven for 8-10 minutes. The edges should be set, but the centers might still look slightly soft and gooey – this is key to their fudgy texture. As soon as they come out of the oven, allow them to cool for 5 minutes on the baking sheet before carefully transferring them to a wire cooling rack to cool completely. It’s absolutely crucial that the cookies are fully cooled before proceeding to the ganache step; otherwise, the warm cookies will melt the ganache right off.

Step 5: Prepare for Ganache. While the cookies are cooling, begin preparing your chocolate ganache. Place your finely chopped semi-sweet or dark chocolate into a medium-sized heatproof bowl. In a separate small saucepan, heat the heavy cream (or double cream) over medium-low heat on the stove. Watch it carefully and remove it from the heat just as it begins to steam and simmer around the edges. Do not let it come to a rolling boil, as this can make the ganache grainy.

Step 6: Make and Apply Ganache. Once the cream is hot, pour it directly over the chopped chocolate in the bowl. Let it sit undisturbed for about 5 minutes; this allows the heat from the cream to melt the chocolate. After 5 minutes, use a rubber spatula to gently stir the mixture in one direction until it becomes completely smooth and glossy. If you still have a few stubborn chocolate chunks, place the bowl in the microwave and heat in 10-second increments, stirring gently after each, until fully melted and smooth. Using a spoon, generously spoon the warm ganache over the completely cooled cookies. Use a small offset spatula or the back of your spoon to gently spread the ganache evenly over the tops of the cookies. Immediately, while the ganache is still wet, sprinkle generously with the rainbow chocolate chips. Allow the ganache to set at room temperature for about 30 minutes, or in the fridge for 15 minutes, before serving. Then, enjoy your homemade cosmic masterpiece!

Ella’s Expert Tips & Tricks for Cosmic Cookie Perfection

• Embrace the Kitchen Scale: I cannot stress this enough – always, always recommend using a kitchen scale when baking, especially for dry ingredients like flour and cocoa powder! Measuring by volume (cups) can be incredibly inaccurate, often leading to too much flour or cocoa powder, which will inevitably result in cookies that are as dry as the desert. A scale ensures precise measurements for consistently perfect, fudgy cookies every time.
• Patience with Cooling: This is a non-negotiable step! Ensure your freshly baked cookies are completely cool to the touch before you even think about adding the luscious ganache topping. If the cookies are even slightly warm, the ganache will melt, slide right off, and create a messy situation instead of a perfectly set, glossy finish.
• Creative Rainbow Chip Swaps: If the specific rainbow chips are elusive, don’t let it deter your cosmic cookie dreams! There are many fantastic alternatives. You can top them with mini chocolate chips for extra chocolatey goodness, opt for baking chips in another exciting flavor (how amazing would peanut butter chips or white chocolate chips be?), use regular rainbow sprinkles (the long, thin jimmie-style or nonpareils work great), crushed candy canes for a festive twist, or even a sprinkle of flaky sea salt for a sophisticated flavor contrast.
• Handle Heavy Cream with Care: When preparing your ganache, it’s vital to heat the heavy cream until it steams and just begins to simmer, but absolutely do not let it come to a rolling boil. If the cream gets too hot before being poured over the chopped chocolate, it can cause the chocolate to seize or separate, resulting in a grainy, unappealing chocolate ganache instead of a smooth, glossy one.
• Room Temperature Ingredients are Key: For the cookie dough, ensure your butter, egg, and egg yolk are at room temperature. This allows them to emulsify properly with the sugars, creating a smooth, cohesive dough that bakes evenly and results in a better texture. Cold ingredients can lead to a lumpy dough and a less uniform cookie.
• Uniform Scooping for Even Baking: Using a cookie scoop (a 3-tablespoon size is ideal for these cookies) is the best way to ensure all your cookies are the same size. This not only makes for a more professional-looking batch but also guarantees that all cookies bake evenly and finish at the same time.
• Don’t Overbake: For that truly fudgy, chewy texture, it’s better to slightly underbake than overbake. The cookies should look set around the edges but still a little soft and underdone in the center when you pull them from the oven. They will continue to set as they cool on the hot baking sheet.

If you’ve made this incredibly delicious recipe and brought a little cosmic joy into your kitchen, please make sure to leave a ⭐️ rating and a thoughtful review below! Your feedback is invaluable and helps other bakers. I absolutely love seeing your culinary creations, so don’t forget to tag me on Instagram @alpineella so I can admire what you’ve made! You can also follow along for more baking inspiration on Pinterest,Facebook and TikTok!

Cosmic Brownie Cookies

Ella Gilbert

Nutrition