Copycat Costco Vanilla Sheet Cake Recipe – Soft, Moist, and Party-Ready

If you love Costco’s famous vanilla sheet cake but want to make it at home, this recipe is your new go-to. It’s fluffy, tender, and layered with a creamy vanilla buttercream that tastes like the real thing. The best part?

It’s designed for a crowd and keeps well, so it’s perfect for birthdays, potlucks, or any celebration. You’ll get that classic bakery-style crumb and smooth frosting without fuss. Simple ingredients, straightforward steps, and big results.

What Makes This Recipe So Good

• Moist, bakery-style crumb: Using oil and butter together creates a soft, tender cake that stays moist for days.
• Even bake in a large pan: This batter is balanced to rise evenly in a 12×18-inch sheet pan, just like a bakery sheet cake.
• Smooth, stable frosting: The American buttercream holds its shape, spreads easily, and has that classic vanilla flavor.
• Great for decorating: The cake slices cleanly and the frosting pipes well for borders and simple designs.
• Make-ahead friendly: Both cake and frosting can be prepared in advance, making party prep easier.

Ingredients

For the Vanilla Sheet Cake

• 3 cups (360 g) all-purpose flour
• 2 cups (400 g) granulated sugar
• 1 tablespoon baking powder
• 1/2 teaspoon baking soda
• 1 teaspoon fine sea salt
• 1 cup (226 g) unsalted butter, softened
• 1/2 cup (120 ml) neutral oil (canola or vegetable)
• 5 large eggs, room temperature
• 1 tablespoon pure vanilla extract
• 1 1/2 cups (360 ml) whole milk, room temperature
• 1/2 cup (120 ml) sour cream, room temperature

For the Vanilla Buttercream

• 1 1/2 cups (339 g) unsalted butter, room temperature
• 6 cups (720 g) powdered sugar, sifted
• 1 tablespoon pure vanilla extract (or 2 teaspoons vanilla bean paste)
• 1/4 teaspoon fine sea salt
• 5–7 tablespoons heavy cream, as needed for texture

Optional for Filling or Garnish

• Thin layer of vanilla pudding or pastry cream
• Fresh berries or sprinkles

Instructions

1. Prep the pan and oven: Heat oven to 325°F (165°C). Grease a 12×18-inch rimmed sheet pan (half-sheet) and line the bottom with parchment. Lightly flour the sides.
2. Mix dry ingredients: In a large bowl, whisk flour, sugar, baking powder, baking soda, and salt until combined.
3. Beat in fats: Add softened butter and oil to the dry ingredients. Mix on medium speed for about 1–2 minutes until the mixture looks sandy and clumps slightly. This coats the flour and helps create a tender crumb.
4. Combine wet ingredients: In a separate bowl, whisk eggs, vanilla, milk, and sour cream until smooth.
5. Build the batter: Pour half the wet mixture into the dry mixture and beat on low until just combined. Add the remaining wet mixture and mix on medium speed for 45–60 seconds until smooth. Do not overmix.
6. Bake: Pour batter into the prepared pan and spread evenly to the corners.Tap the pan gently on the counter to release air bubbles. Bake 25–32 minutes, or until the top is lightly golden and a toothpick comes out clean or with a few moist crumbs.
7. Cool completely: Place the pan on a rack and let the cake cool in the pan. For best texture, cool at least 1 hour before frosting.
8. Make the buttercream: Beat butter on medium-high for 3 minutes until pale and fluffy.Add half the powdered sugar, vanilla, and salt. Beat on low until combined, then add remaining sugar. Stream in heavy cream, 1 tablespoon at a time, and beat 2–3 minutes until light and spreadable.

   Adjust cream or sugar to reach a smooth but stable consistency.

9. Frost the cake: If desired, chill the cake for 20 minutes for easier frosting. Spread a thin crumb coat, chill 10 minutes, then add a thick, even layer of buttercream. Use an offset spatula to smooth. Pipe a border if you like.
10. Optional filling layer: For a classic bakery vibe, spread a very thin layer of vanilla pudding over the cooled cake before frosting. Keep it thin to avoid slipping.
11. Decorate and serve: Add sprinkles, simple rosettes, or a message. Slice into squares and serve slightly chilled or at cool room temperature.

Keeping It Fresh

• Room temperature: The frosted cake keeps well covered at cool room temp for up to 2 days if your kitchen isn’t hot.
• Refrigerator: Store tightly covered for 4–5 days. Let slices sit out 15–20 minutes before serving for the best texture.
• Freezer: Freeze unfrosted cake layers, wrapped well, for up to 2 months. Thaw in the fridge overnight. Buttercream also freezes for 2 months; thaw and rewhip with a splash of cream.
• Make-ahead tip: Bake the cake a day ahead, wrap, and chill. Frost the next day for a clean finish and easier slicing.

Health Benefits

This is a celebratory dessert, so it’s more about joy than nutrition. Still, there are a few bright spots. Whole eggs provide protein and fat-soluble vitamins, and whole milk and butter lend calcium and energy.

Portion control matters most here.

If you’re looking to tweak it, you can slightly reduce sugar in the frosting or swap part of the flour for a fine white whole wheat to add a bit of fiber. Keep in mind, changing ratios can affect texture, so make small adjustments.

What Not to Do

• Don’t overmix the batter: Once the wet and dry come together, mix just until smooth. Overmixing can make the cake dense.
• Don’t skip room-temperature ingredients: Cold eggs and milk can cause a curdled batter and uneven bake.
• Don’t overbake: Pull the cake when the center springs back and a toothpick has a few moist crumbs. Overbaking dries it out fast.
• Don’t overload with pudding: If using a pudding layer, keep it thin so the frosting stays put.
• Don’t frost a warm cake: Warm cake will melt buttercream and create crumbs and slides.

Variations You Can Try

• Almond bakery twist: Replace half the vanilla extract with almond extract for that classic bakery flavor.
• Lemon vanilla: Add 1 tablespoon lemon zest to the batter and 1 teaspoon to the frosting for a bright, fresh note.
• Funfetti: Fold 1/2 cup rainbow jimmies into the batter. Use jimmies, not nonpareils, to prevent color bleed.
• Strawberry filling: Spread a thin layer of strawberry preserves between cake and frosting for a fruity layer.
• Whipped buttercream: Swap half the butter with cream cheese or stabilize heavy cream and fold it into a portion of the frosting for a lighter finish.

FAQ

Can I use a different pan size?

Yes. For two 9×13-inch pans, divide the batter evenly and start checking around 22–26 minutes.

For three 9-inch rounds, reduce bake time and keep a close eye from 18 minutes onward. Always test with a toothpick.

How do I get a perfectly flat top?

Lower, slower baking helps. Bake at 325°F, and if your oven runs hot, use cake strips around the pan to reduce doming.

Level with a long serrated knife only if needed.

Can I make this gluten-free?

Yes, use a quality 1:1 gluten-free baking flour with xanthan gum. Let the batter rest 10 minutes before baking to hydrate the starches, then proceed as directed.

What if I don’t have sour cream?

Use full-fat plain Greek yogurt. It gives similar moisture and a light tang that balances sweetness.

Why is my buttercream gritty?

Powdered sugar wasn’t fully incorporated or wasn’t sifted.

Beat the butter longer at the start, sift the sugar, and add cream gradually. Let the frosting rest 10 minutes, then rewhip for a smoother texture.

How do I slice clean squares?

Chill the frosted cake for 20–30 minutes. Use a long, sharp knife, wipe it clean between cuts, and make confident, straight presses rather than sawing motions.

Final Thoughts

This copycat Costco vanilla sheet cake brings bakery quality to your kitchen with simple steps and reliable results.

It’s tender, rich, and sturdy enough for frosting, writing, and decorations. Whether you’re celebrating a birthday or just want a crowd-pleasing dessert, this cake delivers every time. Keep the ingredients at room temperature, watch your bake time, and enjoy that classic vanilla slice everyone loves.