Momofuku Birthday Cake

birthday cake:
4 cups cake flour or 3 and 1/2 c. AP flour + 1/2 cup cornstarch
3 tsp. baking powder
3/4 cup rainbow sprinkles
1 stick salted butter, room temperature [if you only have unsalted, add 1/4 tsp salt to dry ingredients]
2/3 cup vegetable shortening
2 and 1/2 cups granulated sugar
6 tbsp. light brown sugar, tightly packed
6 large eggs
1 cup buttermilk or almond milk + dash of apple cider vinegar
2/3 cup canola oil
4 tsp. clear imitation vanilla extract

birthday cake crumbs:
1 cup granulated sugar
3 tbsp. light brown sugar, tightly packed
1.5 cup cake flour or 1.5 cups AP flour minus 3 tbl flour + 3 tbl cornstarch
1 tsp. baking powder
3/4 tsp. salt
4 tbsp. rainbow sprinkles
1/4 cup canola oil
1/4 cup nonfat Greek yogurt [can use 1/4 cup oil here instead if you're not feeling the healthy sub]
1.5 tbsp. clear imitation vanilla extract

birthday cake soak:
1/2 cup milk
2 tsp McCormick brand clear imitation vanilla extract [I ran out of clear vanilla here and used regular. This is probably the best place to use regular vanilla if you run out of clear vanilla]

birthday cake frosting:
2 sticks salted butter, room temperature
1/2 cup vegetable shortening
4 ounces cream cheese, room temperature
1/4 cup light corn syrup
2 tbsp clear imitation vanilla extract
2 1/2 cups powdered sugar
pinch baking powder
pinch lime juice (optional)

for the birthday cake:
Preheat the oven to 350. Grease two 9? cake pans and a 9×13 pan extremely well. I used the PAM baking spray with flour on top of non-stick pans and had zero problems. Set aside.

Whisk together the flour, baking powder, and 1/2 cup sprinkles in a small bowl. Set the dry ingredients aside for later.

In the bowl of a stand mixer fitted with the paddle attachment, cream together the butter, shortening, and sugars on medium-high speed for 2 to 3 minutes, scraping down the bowl as needed.

Add the eggs (all at once) and then beat again on medium-high for another 2 to 3 minutes. Scrape down the bowl.

With the mixer on low speed, add the wet ingredients (buttermilk, canola oil, and imitation vanilla) in a steady stream. Increase the mixer to medium-high speed and beat for another 4 to 6 minutes. The mixture should double in size and turn pale. Don’t stop mixing until the mixture is completely homogeneous, with no visible streaks of oil or fat.

With the mixer on low, add the dry ingredients, and mix for another minute or so until the ingredients are just combined.

Pour out the batter into the prepared pans, spreading it out into an even layer. Cover with the remaining sprinkles.

Bake for 30–35 minutes until the cake bounces back slightly when gently pressed in the corner. The center of the cake should no longer jiggle when the pan is shook. Cool the cake completely in the pan on a wire rack.

for the birthday cake crumb:
Preheat the oven to 300 and line a baking sheet with a Silpat or piece of parchment.

In the bowl of a stand mixer fitted with the paddle attachment, combine the sugars, flour, baking powder, salt, and sprinkles. Mix on low speed until combined.

Stream in the oil and the imitation vanilla on low speed and continue beating the mixture until the ingredients clump and form small clusters. Mix in the yogurt, if using. This will make the clusters more sticky and less clumpy, but they will harden after baking!

Carefully spread the clusters in a thin layer on the prepared baking sheet and bake them for about 20 minutes, breaking up occasionally. They will be slightly moist but will harden as they cool. Let them cool completely before using.

for the birthday cake soak:
Whisk together the milk and vanilla in a small cup or bowl.

for the birthday cake frosting:
In the bowl of a stand mixer fitted with the paddle attachment, cream the butter, shortening, and the cream cheese for 2 to 3 minutes on medium-high until the mixture is smooth and fluffy.

Add the corn syrup, and vanilla, and beat the mixture on medium-high speed for 2 to 3 minutes or until the mixture is smooth and glossy white.

Add the powdered sugar, baking powder, and lime juice, if using, on low speed until just combined. Crank the mixer to high speed and beat for 2 to 3 minutes or until the mixture is stark white and fluffy.

assembling the layer cake:
Trim the edges off of the two 9? cake layers. Line one 9? cake pan with enough foil to cover the interior and and hang off the edges so you can lift the cake out later. Grease foil. Crumble the cake from the 9×13 pan into the foil and use your hands to press down into a flat, even layer. This is the bottom layer of the cake.

Dunk the pastry brush in the birthday cake soak and give the layer of scraps a good, healthy bath of half of the soak. [I just kind of poured half of it over the cake]

Spread one fifth of the birthday cake frosting over the base layer. Then sprinkle with one-third of the birthday cake crumbs evenly over the top of the frosting. Use the back of your hand to anchor them in place. Top with another fifth of the birthday cake frosting, carefully spreading it so that it is even, but without disturbing the crumbs.

Ease a sheet of acetate in between the bottom cake layer and the side of the pan until you have a clear ring of acetate at least 9-10 inches tall, or high enough to support the height of the finished cake. Top with a full circle of cake (save the nicest one for the top layer), brush the rest of the cake soak over this layer, top with another one fifth of the frosting, one third of the cake crumbs, and another one fifth of the frosting.

[Alternatively, you could try using a silpat here in place of the acetate to support the cake during freezing. I haven't tried it, but the cake is pretty sturdy and I think mine would have been okay.]

Nestle the remaining cake round into the frosting. Cover the top of the cake with the last fifth of the frosting. Garnish the frosting with the remaining birthday crumbs.

Freeze the cake for at least 12 hours to set the cake and filling and to make the unmolding much easier.)

Three hours before serving, remove the pan from the freezer, and lift the cake out of the pan by the foil edges. Here, it’s easiest if one person gently holds the cake with both hands around the acetate while the other peels the foil off the bottom. Gently peel off the acetate and transfer the cake to a platter or cake stand. Let it defrost in the fridge for a minimum of 3 hours. Wrapped well in plastic, it can be refrigerated for up to 5 days.