Birthday Cake

Ingredients

For the Vanilla Cake

• Nonstick spray
• 4 cups all-purpose or cake flour
• 2 tsp. baking powder
• 1 ½ tsp. kosher salt
• 1 tsp. baking soda
• 1 ½ cups buttermilk
• ½ cup vegetable oil
• 2 tsp. vanilla extract
• 1 cup (2 sticks) unsalted butter, room temperature
• 2 cups sugar
• ½ cup lightly packed light brown sugar
• 4 large eggs
• 4 large egg yolks

For the Chocolate Frosting

• 12 oz. cream cheese, room temperature
• 2 sticks (1 cup) unsalted butter, room temperature 
• 2 cups powdered sugar
• Pinch of kosher salt
• 12 oz. bittersweet chocolate chips, melted and cooled

Directions
For the cake

1. Preheat oven to 350° and position one rack in the top of the oven and one rack in the middle of the oven. Spray three 9-inch cake pans with nonstick spray.
2. In a large bowl, whisk the flour, baking powder, salt, and baking soda together; set aside. In a medium bowl (or a measuring cup), combine the buttermilk, vegetable oil and vanilla extract; set aside.
3. In a large bowl, combine the butter, sugar, and light brown sugar. Using an electric mixer on high, beat everything together until it’s super light and fluffy, about 4 minutes.
4. Add in the eggs and egg yolks one at a time, beating in between additions.
5. Beat the batter until it’s almost doubled in volume and very light and fluffy, about 5 minutes. (Don’t forget to periodically scrape down the sides of the bowl.)
6. With the mixer on low, gently beat in one-third of the flour mixture. Before it’s fully combined, add in one-half of the buttermilk mixture. Repeat with remaining flour and buttermilk until everything is well blended and no lumps remain.
7. Divide the cake batter among the three cake pans and place two pans on the top rack and one pan on the middle rack. Bake 35-40 minutes, rotating the pan on the middle rack up to the top rack halfway through baking, so they all get even oven love.
8. Remove the cakes from the oven and invert them onto a wire baking rack to cool completely. 

For the frosting

1. In a large bowl, combine the cream cheese, butter, sugar, and salt. Using an electric mixer on high speed, beat until everything is fluffy and almost pure white, about 5 minutes. With the mixer on low, slowly add in the melted chocolate and blend. Increase the speed to high and beat until everything is combined and the frosting looks super fluffy and delicious like it came from a can (but it didn’t), about 2 minutes.
2. Once cakes are cooled, use an offset or regular spatula to spread frosting onto the first layer of cake, bottom-side up. (Layering the cake with the flat bottoms on top makes a cake with a neater shape; you can layer and frost the cakes on the wire rack or on a plate.) Repeat with remaining layers. Apply a thin layer of frosting all over the cake, making sure to cover the whole cake. This is called “the crumb coat,” and it’s just the base layer, so don’t worry about making it perfect. Chill the cake for 2 hours, but keep the frosting out at room temperature.
3. Remove the cake from the fridge and using either an offset spatula or a butter knife, give it another coat of frosting, doing whatever decorative patterns or swirls your heart desires. Super smooth, peaks and valleys, whatever you like! Your cake, your call.

Notes
Decorate with sprinkles however you please.

Source
http://www.buzzfeed.com/alisonroman/perfect-birthday-cake