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Homemade Costco Sheet Cake dupe is perfect for parties when you’re craving that signature soft crumb, fluffy mousse center, plus that sweet classic frosting you remember from birthdays. This version lets you bring all those bakery vibes and flavors home, so you don’t need to leave your kitchen.
I first baked this for my kid’s graduation bash and it vanished before I even got another piece. Now, it’s my go-to for every big family moment.
Dreamy Ingredients
- Cream cheese: makes the mousse super creamy and adds a little tang
- Sprinkles: pick whatever colors you want for your party (rainbow’s always a win)
- Vanilla instant pudding mix: keeps the mousse thick and velvety
- White cake mix: gives that light, fluffy texture you expect
- Kosher salt: helps bring out flavor and balances out the sweet stuff
- Vegetable shortening: gives you that real-deal bakery icing that’s easy to pipe
- Pure vanilla extract: use a clear kind if you want the cake bright white
- Sour cream: brings in a moist, tender bite that’s classic
- Heavy cream: makes both the mousse and whipped topping extra airy
- Vegetable oil: helps keep everything tender and soft
- Large egg whites: guarantee the cake is super light and shockingly white
- Whole milk: ups the richness compared to just water
- Confectioners sugar: adds a gentle sweetness and helps the icing stay fluffy
- Quick cake mix tip: Look for one with a really white batter, since some have yellow coloring
Easy Steps
- Frost and Decorate:
- Smooth on a thick layer of frosting with an offset spatula. Scoop extra into a piping bag and make shell borders if you’re feeling fancy. Sprinkle on your favorite toppings.
- Make the Frosting:
- Whip the shortening, a splash of water, a dash of salt, and vanilla until smooth. Add confectioners sugar slowly so it doesn’t go everywhere. Once it’s all in, crank the speed and whip for about a minute until nice and fluffy.
- Build Your Cake:
- Lay down the first cake on your platter. Add the mousse and spread it out but don’t go all the way to the edge—leave about half an inch. Top with the second cake, flat side up. Chill to let the mousse settle.
- Mix the Mousse:
- Beat cream cheese, powdered sugar, and salt until totally smooth, around a minute or two. Then, pour in milk and dry pudding mix, blend another minute. Stream in heavy cream, beat everything on high until it looks fluffy and thick, another minute or two.
- Bake the Cake:
- Pour the batter in each pan and bake at 350°F for around 20-25 minutes. When the cakes are golden and touch back when pressed, take them out. Cool the cakes in their pans for about 10 minutes, then flip onto a rack. Slice any domed tops off once they’re totally cool.
- Mix Up the Batter:
- In your mixer, blend cake mixes with salt. Add egg whites, sour cream, whole milk, vanilla, and oil. Beat for about two minutes until the blend is smooth and a little thick.
- Prep Your Pans:
- Line two 12×9 inch metal pans with parchment. Spray really lightly—it’ll help lift the cake out easily later.
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I’m all about the mousse center. When I was a kid, my mom would hand me the bowl and let me scrape out every last bit. That tangy, sweet flavor stuck with me, so now I always double it if anyone’s coming over.
Storage Secrets
Your cake will stay fresh in the fridge (covered up) for four to five days, super soft. Chill it completely before you slice for the neatest pieces. For a longer stretch, wrap those slices up tight and freeze for a couple months. Let them thaw overnight in the fridge for best texture.
Swaps and Options
You can totally use yellow cake mix if you want a different vibe, just know it’ll taste a bit richer. Try cheesecake pudding instead of vanilla for the filling, it’s great. If you want a less sugary icing, swap half the shortening for butter—though pure shortening is what gives it that old-school stability. For dairy-free friends, just use alternate milks and cream cheese.
Serving Ideas
Fancy it up with piped flowers or pile on some fresh berries after your sprinkles. Keep it cold for sharp slices, or leave it out a bit if you like softer cake. Milk and coffee go great with this, and trust me, nobody’s stopping at one serving.
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Tradition and Hype
Costco sheet cakes are a big deal because they feed a ton of people without breaking the bank. They're a favorite for birthdays, big gatherings, and all kinds of family celebrations. That super light cake and sweet, creamy frosting just remind people of fun times together.
Recipe FAQs
- → What can I do to keep my cake nice and moist?
Go for sour cream and egg whites, and don’t let it stay in the oven too long. Check if it’s done early just to be safe.
- → Could I grab another cake mix flavor instead?
Totally—yellow or chocolate mix works great too. Just know it’ll taste and feel a little different than the all-white classic.
- → How do I get frosting that's super light?
Beat together shortening with powdered sugar until it puffs up. Sprinkle sugar in a bit at a time and keep mixing. That's the trick for fluffiness.
- → Is it okay to build this cake the day before?
Yep! Put the whole thing together and chill overnight if you want. Hold off on frosting and sprinkles until you're ready to serve for the best look.
- → Can I make this if I don’t own a stand mixer?
No problem—a regular hand mixer can handle it all. A stand mixer just makes things quicker when working with big batches.
- → What's the best way to cut neat slices like a pro?
Pop the cake in the fridge to set, then use a sharp, slightly warm knife. Clean the blade after each slice for tidy pieces.