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Best Classic Birthday Sheet Cake with Rainbow Sprinkle Buttercream

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A moist, tender sheet cake topped with a vibrant rainbow sprinkle buttercream. This easy, foolproof recipe is perfect for birthday parties, potlucks, or any celebration, and comes together in under an hour with simple pantry ingredients.

Ingredients

Scale
  • 2 1/2 cups (315g) all-purpose flour
  • 2 1/2 teaspoons baking powder
  • 1/2 teaspoon baking soda
  • 1/2 teaspoon salt
  • 3/4 cup (170g) unsalted butter, softened
  • 1 1/2 cups (300g) granulated sugar
  • 3 large eggs, room temperature
  • 1 tablespoon vanilla extract
  • 1 cup (240ml) buttermilk, room temperature
  • 1 cup (226g) unsalted butter, softened (for buttercream)
  • 4 cups (480g) powdered sugar, sifted
  • 2–3 tablespoons heavy cream or whole milk
  • 1 teaspoon vanilla extract (for buttercream)
  • 1/4 teaspoon salt (for buttercream)
  • 1/3 cup rainbow sprinkles (jimmies)

Instructions

  1. Preheat your oven to 350°F (175°C). Position the rack in the center of the oven. Line a half-sheet pan (13×18 inches) with parchment paper and lightly grease the sides with butter or non-stick spray.
  2. In a large bowl, whisk together the all-purpose flour, baking powder, baking soda, and salt. Set aside.
  3. In the bowl of a stand mixer or using a hand mixer, beat the softened butter and granulated sugar on medium speed for 3 to 4 minutes until light, fluffy, and pale yellow. Scrape down the sides and bottom of the bowl halfway through.
  4. Add the eggs one at a time, beating well after each addition. Add the vanilla extract and beat until combined.
  5. With the mixer on low speed, add about one-third of the flour mixture, then half of the buttermilk. Mix just until combined. Repeat with another third of the flour, the remaining buttermilk, and finally the last third of the flour. Stop mixing when the last streaks of flour disappear. Use a spatula to gently fold the batter from the bottom up to ensure everything is incorporated.
  6. Pour the batter into the prepared pan and spread it evenly into the corners. Tap the pan gently on the counter to release any air bubbles.
  7. Bake for 20 to 25 minutes, or until the top is golden brown, the edges have pulled away from the pan, and a toothpick inserted into the center comes out clean or with a few moist crumbs. Cool the cake in the pan on a wire rack for 10 minutes, then lift it out using the parchment overhang and transfer to the wire rack to cool completely (at least 1 hour).
  8. While the cake cools, make the buttercream: In a clean mixer bowl, beat the softened butter on medium speed for 2 minutes until smooth and creamy. Gradually add the sifted powdered sugar, one cup at a time, beating on low speed. Add the vanilla extract and salt. Add the heavy cream, one tablespoon at a time, until the frosting reaches a spreadable consistency.
  9. Gently fold the rainbow sprinkles into the buttercream using a spatula. Be careful not to overmix.
  10. Once the cake is completely cool, spread the buttercream evenly over the top using an offset spatula. Sprinkle a generous handful of rainbow sprinkles on top and press them in gently.
  11. Slice and serve at room temperature.

Notes

Room temperature ingredients are crucial for best texture. Do not overmix the batter. Let cake cool completely before frosting. Use jimmies (not nonpareils) to prevent color bleeding. Cake can be stored at room temperature for up to 2 days or refrigerated for up to 5 days. Unfrosted cake can be frozen for up to 3 months.

Nutrition

Keywords: birthday cake, sheet cake, rainbow sprinkle buttercream, easy cake, classic cake, party cake, buttermilk cake

Find it online: https://dinadishes.com/best-classic-birthday-sheet-cake-with-rainbow-sprinkle-buttercream/