Birthday Cake

Instructions

For the Cake

1. Preheat the oven to 177°C / 350°F. Pan-spray a quarter sheet pan and line it with parchment paper. 
2. Mix the butter, shortening and sugar in the bowl of a stand mixer fitted with the paddle attachment and stir together for 2-3 minutes on a medium-high. Scrape down the sides of the bowl.
3. Add the eggs, one at a time,  beat for 1 minute after each addition on medium-high. Scrape down the sides of the bowl and stir for 4 minutes with the mixer on high. Scrape down the sides of the bowl again.
4. Combine buttermilk, oil and vanilla and add the mixture slowly on low speed. Increase the speed of the mixer to medium-high and stir for 2-3 minutes until the mixture is white, twice the size of the initial mixture and completely homogeneous. Stop the mixer and scrape down the sides of the bowl.
5. In a medium bowl mix cake flour, baking powder, salt and 50g of rainbow sprinkles together. Add the dry ingredients with the mixer on very low speed. Mix for 45 to 60 seconds until the batter  comes together.  Scrape down the sides of the bowl. Mix again for 45 seconds on low speed.
6. Spread the cake mixture evenly in the pan by using a spatula. Add the remaining rainbow sprinkles on top of the batter.
7. Bake for 30 to 35 minutes on the center rack. Rotate the pan halfway through baking. The cake will rise, doubling in size. 
8. After 30 minutes, gently tap the edge of the cake. The cake should spring back slightly and the center should no longer jiggle. Leave the cake in the oven 3-5 minutes longer if it s not yet ready.
9. Remove the cake from the oven and cool it on a wire rack.
10. Wrap the cake in plastic and keep in the fridge overnight.

For the Frosting

1. In the bowl of a stand mixer fitted with the paddle attachment beat butter, shortening and cream cheese for 2-3 minutes on a medium-high speed, until the mixture is smooth and fluffy. Scrape down the sides of the bowl. 
2. Use the lowest speed of the mixer to add corn syrup and vanilla. Turn the mixer up to medium speed and beat for 2-3 minutes until the mixture is white. Scrape down the sides of the bowl.
3. Add powdered sugar, salt, baking powder and citric acid and mix on low speed to incorporate into the batter. Increase speed to medium-high and beat for 2-3 minutes until you have a white and smooth frosting. 

For the Crumbs

1. Preheat the oven to 149°C /300°F. Line a pan with baking paper.
2. Mix sugar, cake flour, baking powder, salt and sprinkles in the bowl of a stand mixer fitted with the paddle attachment on low speed until well combined.
3. Add the oil and vanilla and paddle to distribute. The wet ingredients act like a glue holding the dry ingredients together into small clumps; continue paddling until this happens.
4. Place the clumps on the prepared baking sheet and bake for 20 minutes.
5. Let the crumbs cool completely before using them. 

Assemble the Cake

1. Put a piece of parchment paper on your work surface. Place the cake onto it and peel the parchment from the bottom of the cake. Use the cake ring to cut out 2 circles from the cake. These are the top 2 cake layers. Use the remaining cake "scrap", put it together to make the bottom layer of the cake.
2. Clean the cake ring and place it in the center of a silpate-lined sheet pan. Use 1 strip of acetate to line the inside of the cake ring.
3. Arrange the cake scraps in the ring and with the back of your hand, push them together to form a flat, even layer.
4. Spoon half of the vanilla soak onto the cake layer.
5. Using the back of a spoon, spread one-fifth of the frosting in an even layer over the cake. 
6. Distribute one-third of the crumbs evenly over the frosting. Anchor them with the back of your hand. 
7. Use the back of a spoon to spread a second-fifth of the frosting as evenly as possible over the crumbs. 
8. Gently insert the second acetate strip with your index finger between the cake ring and the first acetate strip, providing a transparent acetate ring 5 to 6 inches high. Place a cake round on the frosting and repeat the process for layer 1.
9. Place the remaining cake round into the frosting. Spread the rest of the frosting over the top of the cake. Decorate it with the remaining crumbs.
10. Transfer the baking sheet to the fridge and let it cool for at least 12 hours to allow the cake and filling to set. 
11. Remove the sheet from the fridge and release the cake from the cake ring. Carefully remove the acetate and place the cake on a plate. 
12. Slice the cake and serve.