Preheat the oven to 325 degrees F (160 degrees C). Grease and line three 6 inch cake pans with parchment paper.

In the bowl of a stand mixer fitted with the paddle attachment, combine the flour, sugar, baking powder, and salt.

Cut up the butter into small cubes and add to the dry ingredients. Mix on low speed until it resembles wet sand.

Add the oil, buttermilk, egg, and vanilla, and mix until just combined.

Divide the cake batter between the prepared pans.

Bake for 22-25 minutes or until a toothpick inserted comes out clean. Immediately turn the cakes out onto a wire rack to cool completely.

Once cool, wrap the cakes in plastic wrap and freeze until ready to decorate.

In a large saucepan, place the butter over medium heat. As the butter melts, stir it with a rubber spatula to encourage even cooking. Once the butter has fully melted, it will alternate between rapid large bubbles and gentle small foamy bubbles. The butter will be ready once it turns a dark golden color and the fat solids have darkened and settled at the bottom of the pan.

Add the milk chocolate, heavy cream, powdered sugar, cocoa powder, salt, and vanilla. Stir constantly until everything is melted and fully combined.

Pour the mixture through a fine mesh sieve into a large bowl. Press plastic wrap up against the surface and place in the fridge for at least one hour or overnight.

Place the first cake layer on a cake stand. Use a 3 tablespoon cookie scoop to add 3 scoops of frosting. Use an offset spatula to spread into an even layer. Repeat with the next cake layer.

Add the last cake layer and top with a few more scoops of frosting. Use the offset spatula to smooth out the top, and spread the excess all over the sides. Continue decorating the cake as desired.

Top the cake with confetti sprinkles, and enjoy!