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The Best Birthday Sheet Cake with Rainbow Sprinkle Buttercream

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A tender, moist sheet cake topped with thick, creamy vanilla buttercream and a generous shower of rainbow sprinkles. This easy, crowd-pleasing birthday cake comes together in under an hour and feeds a crowd with no fuss.

Ingredients

Scale
  • 2 ¾ cups (345g) all-purpose flour
  • 2 ½ teaspoons baking powder
  • ½ teaspoon baking soda
  • 1 teaspoon fine sea salt
  • 1 cup (227g) unsalted butter, softened
  • 1 ½ cups (300g) granulated sugar
  • 3 large eggs, room temperature
  • 1 extra egg yolk, room temperature
  • 1 tablespoon pure vanilla extract
  • 1 cup (240ml) buttermilk, room temperature
  • 1 ½ cups (340g) unsalted butter, softened (for frosting)
  • 5 cups (600g) powdered sugar, sifted
  • 3 tablespoons heavy cream (or whole milk)
  • 2 teaspoons vanilla extract (for frosting)
  • ⅔ cup rainbow sprinkles (jimmies)

Instructions

  1. Preheat oven to 350°F (175°C). Position rack in center. Line a half-sheet pan (18×13 inches) with parchment paper, leaving 2-inch overhang on long sides. Lightly grease parchment and exposed pan sides with butter or non-stick spray.
  2. In a medium bowl, whisk together flour, baking powder, baking soda, and salt for about 20 seconds. Set aside.
  3. In a large bowl, beat softened butter on medium speed for 2 minutes until pale and fluffy. Add sugar and beat for another 3 minutes. Scrape sides and bottom of bowl. Mixture should look light and almost grainy.
  4. Add eggs one at a time, beating well after each addition. Add extra egg yolk and vanilla extract. Beat on medium speed for 1 minute until smooth and glossy (mixture may look slightly curdled).
  5. With mixer on low speed, add one-third of flour mixture, mixing until just combined. Add half of buttermilk and mix. Repeat with another third of flour, remaining buttermilk, then final third of flour. Stop mixing as soon as last streaks of flour disappear.
  6. Scrape batter into prepared pan and spread evenly. Tap pan gently on counter to release air bubbles.
  7. Bake for 22-26 minutes, until top is golden brown and a toothpick inserted in center comes out with a few moist crumbs. Cool in pan on wire rack for 15 minutes, then use parchment overhang to lift cake out. Cool completely before frosting (about 1 hour).
  8. For buttercream: In a large bowl, beat softened butter on medium-high speed for 5 full minutes until pale, fluffy, and almost white. Reduce speed to low and gradually add powdered sugar, about 1 cup at a time. Add heavy cream and vanilla. Increase speed to medium-high and beat for 2-3 minutes until light and airy. If too thick, add another tablespoon of cream; if too thin, add more powdered sugar.
  9. Gently fold rainbow sprinkles into buttercream with a spatula. Do not overmix. Spread frosting over completely cooled cake in thick, swooping swirls. Add extra sprinkles on top.

Notes

Use jimmies (rod-shaped sprinkles), not nonpareils, to prevent color bleeding. Room temperature ingredients are crucial for best texture. Cake can be made a day ahead; wrap tightly and store at room temperature. Frosting can be made day of. For a 9×13 pan, bake 30-35 minutes. For gluten-free, use a 1:1 gluten-free flour blend with xanthan gum. For dairy-free, use vegan butter and almond milk with apple cider vinegar.

Nutrition

Keywords: birthday cake, sheet cake, sprinkle cake, funfetti, buttercream, easy cake, party cake, rainbow sprinkles

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