Classic Birthday Cake

Ingredients

Yellow Cake

• 2 and 1/2 cups (265 grams) sifted cake flour, such as Glicks 
• 2 teaspoons (10 grams) baking powder
• 1/2 teaspoon baking soda
• 1/2 teaspoon salt
• 3/4 cup (170 grams) unsalted butter, at room temperature
• 1/4 cup (60 milliliters) vegetable oil
• 1 and 2/3 cups (332 grams) granulated sugar
• 3 large eggs plus 1 large egg yolk, at room temperature
• 1/3 cup (80 grams) sour cream, at room temperature
• 1 tablespoon (15 milliliters) Gefen Pure Vanilla Extract
• 1 cup (240 milliliters) whole milk, at room temperature

Chocolate Buttercream

• 1 cup (226 grams) unsalted butter, at room temperature
• 3 cups (360 grams) powdered sugar
• 1/2 cup (45 grams) natural unsweetened cocoa powder, such as Gefen
• 2 tablespoons (30 milliliters) whole milk, at room temperature
• 2 teaspoons (10 milliliters) Gefen Pure Vanilla Extract
• 1/4 teaspoon salt

Topping

• 1/2 cup (100 grams) rainbow sprinkles

Directions

Make the Yellow Cake

1. Preheat the oven to 350 degrees Fahrenheit (177 degrees Celsius). Prepare three six-inch (15-centimeter) or two eight-inch (20-centimeter) round cake pans by spraying the sides with baking spray and fitting a Gefen Parchment Paper circle to the bottom of each pan.
2. In a medium bowl, whisk together the flour, baking powder, baking soda and salt. Set the flour mixture aside.
3. In the bowl of a stand mixer fitted with the paddle attachment, beat the butter at high speed for two minutes, until it is light and creamy. Add the oil and sugar, then mix the ingredients at medium-high speed for two minutes, scraping the bowl and paddle at the halfway point. Decrease the mixer’s speed to low and add the eggs and egg yolk, one at a time, mixing until the ingredients are just combined and scraping the bowl and paddle as needed. Add the sour cream and vanilla, increase the mixer’s speed to high and beat the ingredients for one minute. The mixture will look curdled at this point, but don’t worry—it will become smooth at the end.
4. Turn the mixer off and add the flour mixture all at once. Start the mixer at low speed. Mix the ingredients until they are just combined, then add the milk in a steady stream. Mix until the milk is just incorporated. Scrape the sides and bottom of the bowl and stir the batter a few times to make sure there are no lumps. The batter will be slightly thick.
5. Divide the batter evenly between the prepared cake pans. Bake the cakes for 30 to 35 minutes. They’re done when they spring back to the touch and a toothpick inserted into the centers comes out clean. Let the cakes cool in their pans for five minutes, then remove them from the pans and allow them to cool completely on a wire rack.

Make the Chocolate Buttercream 

1. In the bowl of a stand mixer fitted with the paddle attachment, whip the butter at high speed for about four minutes, until it is creamy and light in color.
2. Scrape the bowl and paddle, then add the powdered sugar, cocoa powder, milk, vanilla and salt. Mix the ingredients at low speed for one to two minutes, scraping the bowl and paddle halfway through the mixing time, until the ingredients are well incorporated.

Assemble the Cake

1. Level the cooled cake layers to your desired height. Fill and stack the layers with Chocolate Buttercream, then crumb coat the cake with Chocolate Buttercream. Chill the crumb-coated cake in the refrigerator for at least 30 minutes to allow the frosting to firm up.
2. Frost a smooth buttercream finish with Chocolate Buttercream, then add a sprinkle border and floating sprinkles to the sides of the cake using the rainbow sprinkles.
3. With the remaining Chocolate Buttercream, pipe a swirl border with a Wilton tip 4B, then garnish the swirls with more rainbow sprinkles.