Prep: 15 minutes
Total: 1 ½ hours
for the batter:
2 cups|447 grams granulated sugar
1 teaspoon vanilla extract
3 large eggs
1 ⅓ cups|275 grams canola oil
1 cup|135 grams all-purpose flour
1 cup|135 grams cake flour
½ teaspoon baking powder
½ teaspoon baking soda
½ teaspoon kosher salt
1 ½ cups|341 grams whole milk
3/4 cup rainbow sprinkles
for the buttercream:
1 ½ cups|350 grams granulated sugar
6 ounces egg whites (about 5 eggs)
36 tablespoons|509 grams unsalted butter, softened
1 teaspoon vanilla extract½ teaspoon kosher salt
1. Make the cake: Heat the oven to 325°F.
2. In a medium bowl, combine the flours, baking powder, baking soda, and salt and set aside. In a stand mixer fitted with a whisk attachment, combine the sugar, vanilla, and eggs and whip until doubled in volume. Drizzle in the oil to emulsify. Alternate adding the dry ingredients and the milk, starting and ending with dry, in 4 additions. Mix to combine, scraping down the sides as needed.
3. Line 3 (8-inch) round cake pans with parchment paper and spray with PAM. Divide the batter between the 3 pans and sprinkle about 3 tablespoons on the top of each, then swirl them in to mix. Bake immediately for about 20 minutes, until set in the center and lightly colored. Cool completely.
4. Make the buttercream: In a medium saucepan, combine the sugar and 3 tablespoons water and set thermometer for soft ball stage.
5. Meanwhile, in a large bowl, whisk the egg whites to medium-stiff peaks on highest speed. When the sugar reaches 240°, with the motor still running, drizzle the sugar into the whites. When the mixing bowl has cooled slightly, begin adding the butter, a few ounces at a time. Continue whipping until the mixtures is uniform and fluffy, scraping down as needed. Add the vanilla and salt and set aside.
6. To assemble the cake, place one layer on a plate. Top with about 1 cup of frosting, spreading it into an even layer. Top with another cake layer and another cup of frosting, then the final cake layer. Spread the frosting all over the top and sides of the cake, then “dust” the sides with the remaining sprinkles.