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Birthday sheet cake with fluffy white frosting and colorful sprinkles on top, decorated with piped borders and served on a wooden board.

Easy Birthday Sheet Cake with Fluffy Frosting for Parties - A Crowd-Pleasing Classic

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Prep Time 30 minutes
Cook Time 30 minutes
Cooling & Frosting Time 2 hours
Total Time 3 hours
Course Cake, Dessert
Cuisine American
Servings 20 Squares

Ingredients
  

  • 2 1/2 cups (300 g) all-purpose flour
  • 2 cups (400 g) granulated sugar
  • 2 1/2 tsp baking powder
  • 1/2 tsp baking soda
  • 1 tsp fine salt
  • 1 cup (240 ml) buttermilk (see note below for substitute)
  • 3/4 cup (170 g) unsalted butter, melted and slightly cooled
  • 1/2 cup (120 ml) neutral oil (canola or vegetable)
  • 4 large eggs, room temperature
  • 1 tbsp pure vanilla extract
  • Optional: 1/2 tsp almond extract for a nostalgic bakery flavor
  • 1 cup (225 g) unsalted butter, room temperature
  • 4 cups (480 g) powdered sugar, sifted
  • 1/4 cup (60 ml) heavy cream or whole milk, plus more as needed
  • 2 tsp pure vanilla extract
  • Pinch of fine salt
  • Optional: 1/4 tsp almond extract
  • Rainbow sprinkles for decorating

Instructions
 

  • Prep the pan: Heat oven to 350°F (175°C). Grease a 9x13-inch metal baking pan and line the bottom with parchment for easy removal.
  • Mix dry ingredients: In a large bowl, whisk flour, sugar, baking powder, baking soda, and salt until combined.
  • Whisk the wet: In another bowl, whisk buttermilk, melted butter, oil, eggs, vanilla, and almond extract (if using) until smooth.
  • Combine: Pour the wet mixture into the dry. Whisk or stir with a spatula just until you no longer see dry flour. Do not overmix—a few small lumps are fine.
  • Bake: Pour batter into the pan and smooth the top. Bake 28–34 minutes, until the top springs back and a toothpick comes out clean or with a few moist crumbs.
  • Cool completely: Set the pan on a rack. Let the cake cool fully before frosting, about 1–2 hours.
  • Make the frosting: Beat butter on medium-high for 2–3 minutes until pale and fluffy. Add half the powdered sugar, vanilla, almond extract if using, and salt. Beat on low to combine, then on medium. Add remaining sugar and 3 tbsp cream. Beat until light and billowy, 2–3 minutes. Add more cream 1 tsp at a time if needed. You want spreadable, fluffy frosting that holds soft peaks.
  • Frost and decorate: Spread frosting over the cooled cake with an offset spatula. Add sprinkles. For clean slices, chill 15 minutes before cutting.
  • Serve: Cut into 15–24 squares, depending on your crowd.