Makes one 6-inch, round 3-layer cake.
Three moist layers of blueberry buttermilk cake, filled with fluffy cream cheese filling and frosted with a rich navy blue bakery frosting all topped with stunning Sweetapolita "Internet Boyfriend" sprinkles!
Preheat the oven to 350℉ (180℃). Grease the bottoms of three 6 x 2-inch round cake pans using a baking spray or with butter and parchment rounds.
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 once piece at a time. Beat until all of the butter is incorporated, about 3 minutes. The mixture should have a crumbly, cornmeal-like texture.
In a medium measuring cup with spout, combine half of the buttermilk and the vanilla bean paste. In a separate measuring cup, gently whisk the eggs and remaining buttermilk.
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.
Toss the blueberries with a little flour and fold them into the batter. Divide the batter evenly among the prepared pans.
Bake two pans in the centre of the oven until a wooden pick inserted into the centre comes out with just a few crumbs, 25-30 minutes (this can vary depending on your oven). Repeat with the final layer. Let the cake layers cool in their pans on a wire rack for 10 minutes. Using a knife, loosen the side of the cakes and carefully turn them out onto wire racks. Peel off the papers (if you used parchment rounds) and let cool completely.
The cake layers will keep wrapped tightly in plastic wrap at room temperature for up to 2 days.
In the bowl of an electric mixer fitted with the paddle attachment, beat the butter, confectioners' sugar, vanilla, lemon juice and salt on medium speed until fluffy, about 5 minutes. Reduce the speed to medium-low, add the cream cheese, and beat until smooth, about 1 minute. (Be sure not to over-beat at this stage, or it will break down the cream cheese into a very thin consistency).
The frosting will keep covered at room temperature for up to 6 hours, and then refrigerated in an airtight container for up to 3 days. Bring chilled frosting to room temperature and beat on low speed to soften.
In the bowl of an electric mixer fitted with the paddle attachment, beat the butter and salt on medium speed until very pale and creamy, about 8 minutes. Gradually add the confectioners' sugar, cream, vanilla and almond extract.
Reduce the speed to the lowest setting and beat for 1 minute. Increase the speed to medium-high and beat until very light and fluffy, about 6 minutes.
Add the food colouring, and beat on medium speed until well incorporated. The colour will darken as it sits, so let stand for about 10 minutes and assess colour. Add additional drops of each colour, if desired.
The frosting will keep in an airtight container in the refrigerator for up to 3 days. Bring chilled frosting to room temperature and beat on low speed to soften. If necessary, you can warm the frosting in a heatproof container in the microwave in 10-second intervals, stirring after each one, until smooth and spreadable.
Put your first cake layer top-up on an 6" round cake board or 8" plate, and spread one-half of the cream cheese frosting on top. Repeat with remaining layers, placing the third cake layer top-down. Make sure that your layers are straight and lined up with the ones below. Wrap the cake in plastic wrap and chill for at least 15 minutes.
Remove the cake from the fridge and, using a turntable, if possible, frost entire outside of cake with a thin layer of the navy blue frosting to seal in the crumbs. Chill until the frosting begins to firm-up, about 30 minutes.
Remove the cake from the fridge and return it to the turntable. Cover the cake with a thick, even and smooth layer of the navy frosting using an offset spatula, reserving about 1 1/4 cups of frosting for the piped top border. Return the cake to the fridge and chill for another 20-30 minutes.
You will want the frosting for the buttercream "poof" border to be very soft, in order to achieve the appealing peaks. If your frosting is more firm at this point, warm frosting in a small heatproof bowl for about 8-10 seconds, and stir, otherwise you will skip the heating step. Fill a pastry bag fitted with a large plain round tip with the softened frosting and pipe some buttercream "poofs" around the top perimeter of the cake.
While your cake is still chilled but slightly tacky to the touch, pour your sprinkles into a medium bowl and gently press sprinkles onto the bottom third of the cake, all the way around, letting the excess fall back into the bowl. You can also put the cake on a cookie sheet and let the excess sprinkles fall onto the sheet. Return the cake to the fridge until the buttercream poofs are very firm, about 30 minutes. Pour more sprinkles atop the flat exposed surface of the top of the cake. Cake will keep covered at room temperature for up to 3 days. Serve at room temperature.