Name: Big Batch Confetti Cake with Buttercream Frosting
Prep time: 20 min
Cook time: 37 min
Total time: 57 min
Ingredients: 3 boxes white cake mix (Use without any additional ingredients as per box instructions.); 3 boxes vanilla instant pudding mix (This adds moisture and structure.); 3 cups whole milk (For added moisture.); 12 large eggs (Provides stability.); 1 cup unsalted butter, melted (Let it cool before mixing.); 1 cup rainbow sprinkles (Mixed into the batter.); 3 cups unsalted butter, softened (Ensure butter is at room temperature.); 3 pounds powdered sugar (Approx. 11 cups, sifted if desired.); 9 tablespoons whole milk (To adjust consistency of frosting.); 3 tablespoons vanilla paste or vanilla extract (For flavor.); 1.5 teaspoons salt (Balances sweetness.); 1/4 cup rainbow sprinkles (For decoration on top.)

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I still remember the first time I made this for a packed backyard party: the kitchen smelled like warm vanilla and everyone gathered around the big sheet pan like it was a fireworks display. That moment—kids with frosting on their cheeks, adults stealing a corner piece—made me obsessed with scaling up favorites. This is my Big Batch Confetti Cake with Buttercream Frosting, the one I turn to when I need to feed a crowd without fussing with dozens of small cakes.

How I first stumbled on this giant party cake

I started with three boxes of white cake mix and three boxes of vanilla instant pudding mix because I wanted structure and extra moisture; the pudding is my shortcut to bakery-like texture. For liquid I use three cups whole milk and I always add 1 1/2 teaspoons vanilla paste or vanilla extract for a deeper flavor. There are 12 large eggs in the batter for stability in a large pan, and I melt one cup unsalted butter, let it cool, and fold it in. To make it cheerful, one cup rainbow sprinkles goes into the batter, and later I top the finished cake with about 1/4 cup sprinkles for decoration.

If you want to read a version of this turned into a different pan or inspiration for size, I once compared mine to a more traditional recipe and noted the differences on my favorite recipe roundup, which you can find at this big-batch confetti cake link that I used while experimenting.

The ingredients that make it sing and what they do

I like to say the whole thing balances rich and light: the boxed white cake mix gives dependable volume, the vanilla instant pudding mix keeps it tender and moist, and the melted unsalted butter gives a toasty richness you can smell as it bakes. For the frosting you need three cups unsalted butter, softened, and three pounds powdered sugar (about 11 cups) to build that thick, pipeable buttercream. Nine tablespoons whole milk help you loosen the frosting in stages, and three tablespoons vanilla paste or vanilla extract adds fragrance. Finally, 1.5 teaspoons salt rounds everything out and prevents the buttercream from tasting overly sweet.

A tiny tip I learned early: always let the melted butter cool before adding it to the eggs and milk. If it is too warm you’ll end up cooking the eggs slightly, and nobody needs scrambled eggs in their confetti cake.

Mixing, baking, and the little tricks I swear by

First, heat the oven to 350°F and prepare a Big Batch Pan or large sheet pan with baking spray. Use an extra-large bowl to whisk together the three boxes of white cake mix and the three boxes of vanilla instant pudding mix so everything is evenly combined. Meanwhile, melt one cup unsalted butter and let it cool. In a separate bowl, lightly whisk the 12 large eggs. When the butter has cooled, combine the cooled butter, the eggs, the three cups whole milk, and 1 1/2 teaspoons vanilla paste or vanilla extract, then mix that with the dry ingredients until just combined—overmixing is an easy way to a denser cake.

Gently fold in the one cup rainbow sprinkles; I fold slowly so the colors don’t bleed into the batter. Pour the batter into the prepared pan and spread it evenly, then tap the pan a few times to release any air bubbles. Bake for 33 to 37 minutes, or until a wooden pick comes out clean. You want the top to be springy and the edges to pull away slightly—that’s how I know it’s done right. Cool completely on a wire rack before frosting, because warm cake will melt the buttercream and turn your neat finish into a glossy mess.

Personal tip: if you want the sprinkles to stay bright, toss them briefly in a teaspoon of flour before folding in. That helps prevent them from sinking and from melting into streaks. Another tip: because this is a big pan, rotating it halfway through can even out browning if your oven has hot spots.

The buttercream that holds up on a crowd-sized cake

For the frosting, beat the three cups unsalted butter until creamy. I alternate mixing in the powdered sugar and the nine tablespoons whole milk in three batches so the sugar doesn’t fly everywhere and the texture builds gradually. After all the powdered sugar is incorporated, add three tablespoons vanilla paste or vanilla extract and 1.5 teaspoons salt, mixing until combined. If the frosting seems too stiff, add a little more milk by the teaspoon; if it is too soft, a few minutes in the fridge will firm it up. Frost the cooled cake generously and shower the top with the remaining 1/4 cup sprinkles.

One of my tricks when covering a large, flat cake is to crumb-coat once, chill for 15 to 20 minutes, then put on the final, smooth layer. It saves time cleaning up excess crumbs, and the finish looks so much cleaner.

What to serve it with, how to save leftovers, and a couple of playful swaps

This cake is brilliant with cold milk, a simple cup of coffee, or a scoop of vanilla ice cream if you want to be decadent. If you’re serving a crowd who likes variety, fresh berries on the side add bright acidity.

Leftovers keep well. If you plan to eat within a few days, cover the pan tightly with plastic wrap and refrigerate; the frosting benefits from chilling and the cake won’t dry out. For longer storage, slice into portions and freeze individually wrapped; thaw in the fridge overnight before serving.

If you want to play with the idea, try 2-3 variations: swap in lemon zest and a tablespoon of lemon juice for a citrus confetti, or drop 1/2 cup cocoa powder into the mix and use chocolate sprinkles for a chocolaty version. If you like floral notes, consider a lavender take—I’ve played around with a lavender buttercream frosting idea when I wanted something delicate and adult-friendly, inspired by a recipe I bookmarked a while ago.

A memory that always makes me smile: the first time I added edible glitter because the birthday girl wanted it to "sparkle like her dress." It turned a simple crowd cake into something that looks celebratory in the most literal way.

Conclusion

If you’re looking for a compact project that feeds a lot of people and still delivers on nostalgia and color, this recipe is my go-to. For a smaller, decorative spin you can compare ideas like the Mini Funfetti Cake with Vanilla Buttercream – Cloudy Kitchen to inspire single-serve versions or party favors.