1/2cuprainbow sprinkles (see post for more info on this)
For the Buttercream Frosting:
1and 1/2 cups unsalted butter, VERY soft
4cupsconfectioners' sugar, sifted
2tablespoonsheavy cream (more if needed)
2teaspoonsbourbon OR vanilla extract (optional; see post for more on this)
Sprinkles, for decorating
To brown the butter:
Place the butter in a small sauce pan over medium-high heat and cook for about 3 minutes – stirring almost constantly – until the butter has turned an amber gold/brown and smells slightly nutty. Remove from heat and pour the butter into the mixing bowl you'll be making the cake batter in. Place the bowl in the refrigerator or freezer and bring the butter back to room temperature. You’ll know the butter is at room temperature when you press a finger into the top and it makes a slight indentation. It should be solid but soft.
Once the butter is at room temperature, make your cakes.
For the Brown Butter Funfetti Cake:
Preheat oven to 350 degrees (F). Cut out two 9-inch round segments of parchment paper to line your cake pans with. Spray each pan generously - sides and bottom - with nonstick cooking spray, then place the parchment paper cut out in the bottom of the pans and spray again. It's important to make sure every bit of pan and paper are sprayed so your cakes don't get stuck. Set pans aside.
In a large bowl using a handheld electric mixer (or in the bowl of a stand mixer fitted with the paddle attachment), combine the brown butter, both sugars, and vanilla extract; beat on medium speed until light and fluffy, about 5 minutes (don't skimp on time here!). Add in the eggs, one at a time, beating well after each addition, and scraping down the sides of the bowl as needed. Set aside.
In a separate bowl, whisk together the flour, cornstarch, baking powder, baking soda and salt, mixing well to evenly combine the ingredients. Add the dry mixture into the wet ingredients and mix on low speed until everything is just barely combined; about 15 seconds. You should still see some lumps and dry streaks. Turn mixer off. Add in the sour cream and milk and using a rubber spatula, fold the ingredients into the mixture, mixing until everything is incorporated, but being sure not to overmix. Set aside. Add the sprinkles and fold in by hand, using a rubber spatula, until just combined. Again, be sure not to overmix! Overmixing is very easy to do, and will result in a dry, dense cake.
Divide the batter evenly among the prepared pans and bake for 33-35 minutes, or until the tops are firm and slightly golden, and a cake tester (or toothpick) inserted in the center comes out clean, or with a few moist (but not wet) crumbs clinging to it.
Allow the cakes to cool in the pans for 5 minutes before gently running a knife around the edges to loosen any stuck bits, then turning them out onto a cooling rack to cool completely.
While the cakes cool, you can make the frosting.
For the Buttercream Frosting:
In a large bowl using a handheld electric mixer (or a stand mixer fitted with the paddle attachment) beat the butter on medium-speed until light and fluffy, about 3 minutes. Reduce the speed to low, then add in the confectioners' sugar; beat until combined. Add in the heavy cream, salt, and bourbon (if using); increase the speed back to medium and continue beating the frosting until very light and fluffy, about 2-3 minutes. If the frosting seems too thin, add a little more confectioners' sugar, starting with one tablespoon at a time; if the frosting seems to thick, add in a little more heavy cream, starting one tablespoon at a time.
When the cakes have completely cooled, place one round on a cake stand or large plate; spread the top and sides evenly with frosting, then gently place the other cake round on top of the frosted one and press down very lightly to seal them together. Continue frosting the cake, using a thin spatula, offset spatula, or whatever you have that works best, until the top and sides of the cake are evenly frosted. Decorate with rainbow sprinkles.
The frosted cake will stay fresh, when stored in the refrigerator, for 3 days. Simply take it out of the fridge an hour or two before serving so it can come to room temperature. It's also yummy cold, especially with a cup of coffee ;)
Be sure not to pack your flour when meausring *Be sure to bring all cold ingredients to room temperature *The frosted cake will stay fresh, when stored in the refrigerator, for 3 days. *recipe and photographs updated 4/21/2016