Homemade cosmic brownies: a complete copycat recipe

These homemade cosmic brownies come down to three things done in the right order: a dense, intentionally underbaked brownie base, a chocolate ganache cooled past the pourable stage, and candy-coated chips pressed on while that ganache still has enough give to grip them. Skip the order and the failure is specific. A warm base melts the ganache into the crumb instead of leaving a distinct layer, and candy shells dropped onto ganache that's still warm turn hazy instead of glossy.

This cosmic brownies recipe adapts the structure of a copycat version of Little Debbie's treat from Persnickety Plates, built with real butter, melted chocolate, and a cream-based ganache. The butter, oil, and chocolate chip amounts below come directly from that published recipe. The egg, yolk, flour, and sugar quantities are this guide's own adaptation, matched to the fudgy-brownie formula a baking-science breakdown from Popular Science lays out: more fat and yolks than whites, minimal flour, no leavening, mixed just until combined. That adaptation hasn't been tested the way a published recipe card has, so treat the stated yield, bake time, and texture notes below as a close starting point, and lean on the visual and toothpick cues in each step rather than the clock.

This guide covers one complete 9x13 version, start to finish, plus troubleshooting for the most common copycat mistakes. It's beginner-friendly and doesn't call for a stand mixer.

Quick reference:

• Yield: intended to make about 18 bars
• Pan: metal 9x13-inch
• Bake: 30 to 35 minutes, judged by a toothpick rather than the clock
• Hands-on time: about 30 minutes
• Total time: about 2 hours 30 minutes, mostly cooling and chilling

What you'll need for homemade cosmic brownies

Brownie base (9x13 pan, about 18 brownies):

• 8 tablespoons (1 stick) unsalted butter
• ½ cup vegetable oil
• 8 ounces (225 grams) semisweet chocolate chips, melted with the butter and oil
• 1 cup granulated sugar
• ¾ cup packed light brown sugar
• 1 teaspoon vanilla extract
• ½ teaspoon salt
• 3 large eggs plus 2 large egg yolks
• 1¼ cups all-purpose flour
• No baking powder or baking soda

Combining butter and oil rather than relying on just one fat is deliberate. More total fat built into the batter means a richer, fudgier brownie, whether that fat comes from butter or oil, per Popular Science's breakdown of brownie chemistry. The extra yolks and brown sugar push this base toward dense and chewy instead of light and cakey: yolks add fat, and brown sugar's molasses content builds chew that granulated sugar alone doesn't, according to the same source.

Ganache:

• ½ cup heavy cream
• 1½ cups semisweet chocolate chips

Heavy cream is required for a ganache that firms up enough to slice; lower-fat dairy like milk or half-and-half won't set the same way, according to The Toasty Kitchen. Persnickety Plates pairs that cream with 1½ cups of chocolate chips, and that's the ratio this guide follows. For a smoother melt, The Toasty Kitchen recommends chopped semisweet baking bars, such as Ghirardelli or Baker's, over chips, since chips are built to hold their shape in baking and can turn slightly grainy when melted this way instead. That source's own ratio runs closer to equal parts cream and chocolate by weight, a different balance than the chip version above, so treat a baking-bar swap as its own variation to test rather than a direct substitute.

Topping:

• ¼ cup rainbow candy-coated chocolate chips, sold as "confetti chips" or "cosmic sprinkles" in the cake decorating aisle or online, per Persnickety Plates and Preppy Kitchen

This DIY method relies on candy-coated chocolate chips for the topping, not plain chocolate chips, which won't give the speckled, rainbow look the recipe is going for.

Tools: a 9x13-inch metal pan, parchment paper, a large mixing bowl, a microwave-safe bowl for melting the butter, oil, and chocolate and for heating the cream, a whisk, a rubber spatula, an offset spatula or butter knife for spreading ganache, and a toothpick.

This recipe is timed for a metal pan, which heats faster and gives firmer edges than glass or ceramic. Glass and ceramic hold heat longer and can bake unevenly, per Popular Science's breakdown, so if that's what's on hand, go by the toothpick test rather than the stated bake time. This recipe also isn't written as a half batch: halving three eggs and two yolks doesn't divide evenly, and dropping to an 8x8 pan changes depth and timing in ways this formula hasn't been tested for. Baking the full batch and freezing half, as described under storage below, sidesteps guessing at that conversion.

Most of the elapsed time is hands-off: about an hour of room-temperature cooling for the brownie base, 20 minutes refrigerated for the ganache to firm up before the candy chips go on, and 10 more minutes after that for the final set.

Step-by-step method

1. Preheat the oven to 350°F and line the pan with parchment, leaving overhang on two sides so the finished slab lifts out easily later.

2. Whisk the granulated sugar, brown sugar, vanilla, salt, eggs, and egg yolks together in a large bowl until smooth. The extra yolks push the texture toward rich and dense instead of light and cakey.

3. Melt the butter, oil, and chocolate chips together in a microwave-safe bowl in 30-second intervals, stirring between each, until smooth. Let the mixture cool until warm rather than hot before whisking it into the egg mixture.

4. Fold in the flour with a spatula, mixing just until no dry streaks remain. Overmixing after the flour goes in builds gluten, which lightens the texture, so stop as soon as the streaks disappear.

5. Pour the batter into the pan and bake 30 to 35 minutes. Look for edges that have set and pulled slightly from the pan sides and a shiny, crackly top. Check the center with a toothpick: a few moist crumbs clinging to it signal a fudgy center, a clean toothpick means a cakier one, and wet batter still stuck to it means the pan needs more time. The brownies keep cooking briefly once out of the oven, a process Popular Science calls carry-over cooking, so don't chase a fully clean toothpick if fudgy is the goal.

6. Cool the brownies completely in the pan, about 1 hour, until the pan is no longer warm to the touch. A warm base will soften the ganache instead of letting it sit as a distinct layer on top.

7. Make the ganache: heat the heavy cream until steaming but not boiling, then pour it over the chocolate chips. Let it sit undisturbed for 2 to 5 minutes before stirring until smooth and glossy. It will look thin at this stage; ganache slowly firms up as it cools.

8. Pour the ganache over the cooled brownies, spread it into an even layer, and refrigerate about 20 minutes. The surface should look mostly set but not hard, the visual cue that matters more than the clock. That window is what the next step depends on.

9. Sprinkle the candy-coated chips over the ganache and press gently so they adhere. Adding them while the ganache is still hot can cause the candy shells to bloom into a hazy, dull finish, which is why this recipe times the chips for after the ganache has cooled and mostly set.

10. Chill another 10 minutes until the ganache is fully set, then lift the slab out using the parchment overhang. Use a sharp knife, wiping it clean between cuts, for squares that stay neat instead of smearing the topping.

Troubleshooting homemade cosmic brownies

Brownies turned out cakey. Too much flour or mixing too long after the flour went in both build gluten and lighten the texture, and baking well past the moist-crumb stage until the toothpick comes out fully clean pushes it further toward cakey too.

Brownies turned out greasy or overly soft. This recipe's butter-and-oil combination is intentional, built to deliver the richness of added fat without tipping into greasy territory. If the base turns out greasy or overly soft, double-check the butter, oil, and chocolate measurements before anything else: too much fat relative to the flour and eggs is the usual cause, and this recipe's balance depends on hitting those amounts as written.

Ganache is still pourable after 20 to 30 minutes of chilling. Give it more time first; ganache firms up gradually and can take longer in a warm kitchen. If it's still soft after that, rewarm it gently and stir in a little extra finely chopped chocolate before re-chilling. This makes the topping firmer and may shift its sweetness depending on the chocolate used.

Candy chips look hazy instead of glossy. They went on while the ganache was still hot; wait for the mostly-set stage described in step 8 next time.

Can't find rainbow candy-coated chips. Similarly sized mini candy-coated chocolates work as a substitute. Plain rainbow jimmies are another option, though it's best to wait until the ganache has fully set in step 10 before adding them.

Storing and serving homemade cosmic brownies

A finished batch should look like clean, set squares with a glossy ganache top and a dense, crumbly-but-cohesive brownie base underneath. Cream can spoil at room temperature, so for the most conservative storage approach, refrigerate the brownies because the topping contains dairy. None of the recipes behind this guide cite a formal food-safety standard for this specific treat; Persnickety Plates allows a covered day or two at room temperature even though its own author prefers the fridge, and Preppy Kitchen calls a couple of days at room temperature fine. Treat both as individual recipe preference rather than a safety ruling, and when in doubt, keep the brownies covered in the refrigerator and eat them within about 4 days, the window Persnickety Plates gives for this topping.

If the ganache firms up too much in the fridge to bite through comfortably, let individual brownies sit at room temperature for a few minutes before serving. Microwaving tends to melt the ganache unevenly instead of just softening it, so skip that shortcut.

For longer storage, wrap brownies individually and freeze. Estimates from the recipes behind this guide range from two to three months; plan on the shorter end if texture matters to you, and thaw in the fridge or at room temperature before serving.