Best Buttermilk Birthday Cake

3 layers of super-moist, vanilla buttermilk cake filled with fluffy white frosting and sprinkles. (Cake layers from The Sweetapolita Bakebook, and the frosting is adapted from Momofuko Milk Bar Cookbook). 

Servings: 12
Ingredients
For the Buttermilk Cake layers:
  • 3 cups (350g) cake flour
  • 2 cups (400g) superfine sugar
  • 1 tbsp + 1 tsp baking powder
  • 3/4 tsp salt
  • 1 cup (227g/2 sticks) cold unsalted butter, cut into pieces
  • 1 1/2 cups (360ml) buttermilk, room temperature
  • 2 tsp (10ml) vanilla bean paste or pure vanilla extract you can also use seeds from 1/2 vanilla bean
  • 1/4 tsp pure almond extract
  • 5 whole eggs, room temperature
For the Birthday Cake frosting:
  • 1 cups (230g/2 sticks) unsalted butter, room temperature
  • 1/2 cup (100g) vegetable shortening
  • 3 tbsp (45ml) clear corn syrup (see notes)
  • 1 tbsp (15ml) pure vanilla extract
  • 1/8 tsp lemon extract
  • 2 1/2 cups (400g) confectioners' sugar
  • 1/2 tsp fine salt
  • 1/2 cup (110g) cream cheese, softened
  • 1/2 cup (4oz) sprinkles, preferably jimmies + coated chips (I used Sweetapolita Sugar Cookie medley)
  • Few drops turquoise gel color (see notes)
Special Tools:
  • Piping tip Ateco #887
  • 18" piping bag
Instructions
For the Buttermilk Cake layers:
  1. Preheat the oven to 350℉ (180℃). Grease the bottoms of three 8 x 2-inch round cake pans and line with parchment.

  2. In the bowl of an electric mixer fitted with the paddle attachment, whisk together the flour, sugar, baking powder, and salt. With the mixer running on low speed, add the cold butter one piece at a time. Beat until all of the butter is incorporated, about 3 minutes. The mixture should have a fine crumble, cornmeal-like texture.

  3. In a medium measuring cup with a spout, combine 1 cup (240ml) of the buttermilk, vanilla and almond extract. In a separate measuring cup, gently whisk the eggs and remaining buttermilk.

  4. Increase the mixer speed to medium-low. Gradually add the vanilla mixture and beat for 5 minutes. Scrape the sides and bottom of the bowl with a rubber spatula. Reduce the mixer speed to low and gradually add the egg mixture in three additions, scraping the sides of the bowl after each addition. Beat until well combined, 2 minutes. Fold the batter once or twice to ensure everything has been incorporated. Divide the batter evenly among the prepared pans.

  5. Bake the first two layers in the centre of the oven until a wooden pick inserted into the centre comes out with a few crumbs, 20 to 22 minutes. Repeat with the final layer. Let the cake layers cool in their pans on wire racks for 10 minutes. Using a knife, loosen the sides of the cakes and carefully turn them out onto wire racks. Peel off the paper liners and let cool completely. 

  6. The cake layers will keep wrapped tightly in plastic wrap at room temperature for up to 3 days.

For the Birthday Cake frosting:
  1. Combine the butter and shortening in the bowl of a stand mixer fitted with the paddle attachment (or a regular mixing bowl if you are using a hand-held mixer), and beat on medium-high speed for about 3 minutes, until the mixture is creamy and fluffy. Scrape down the sides of the bowl. 

  2. With the mixer on low speed, stream in the corn syrup, vanilla and lemon extract. Turn the mixer up to medium-high, and beat for 3 minutes. Scrape down the sides of the bowl. 

  3. Add the confectioners' sugar and salt and beat on low speed until incorporated. Turn the mixer back up to medium-high and beat for 3 more minutes, until you have shiny, creamy, smooth frosting. 

  4. Add the softened cream cheese, and beat on medium speed until combined, about 1 minute. Don't over-beat, or the frosting will become too thin (due to the cream cheese). 

  5. Frosting will keep in an airtight container in the fridge for up to 1 week. Bring to room temperature and beat on low speed 

Assemble the Buttermilk Birthday Cake:
  1. Place one of the cake layers, top up, on a cake board or plate (reserve the "sharpest" edged layer for the top). Using a small offset palette knife, spread 1 1/4 cups of the frosting top, extending slightly past the cake's edge. Sprinkle the layer of frosting with some of the sprinkles. Repeat these steps until you come to the final cake layer, which you will place bottom up. Using a straight palette knife, smooth the frosting protruding from the layers on the sides of the cake. Chill for 15 minutes.

  2. Remove the cake from the refrigerator, and apply a thin layer of frosting over the cake to seal in crumbs (known as the crumb coat). Return the cake to the refrigerator and chill until the frosting is slightly set, about 15 minutes. 

  3. While the cake is chilling, scoop out about 2 cups of the remaining frosting and tint it very pastel turquoise (about 1 drop). Add the rest of the sprinkles to the remaning white frosting. Fit an 18" pastry bag with a large closed star tip (I use Ateco #887) and transfer the turquoise frosting to the bag. 

  4. Remove the cake from the refrigerator and apply a smooth, thick layer of the sprinkled frosting. Pipe a border around the top perimeter. 

  5. The cake will keep at room temperature for up to 12 hours. Refrigerate for up to 3 days, but serve at room temperature if possible. 

Sweetapolita's Notes