Preheat the oven to 350F and grease two 8 inch round metal baking pans well. Line the bottoms with parchment paper and grease the parchment.
In a medium bowl, whisk together the almond flour, protein powder, baking powder, and salt.
In a large bowl, beat the butter with the sweetener until lightened and fluffy, about 2 minutes. Beat in the eggs one at a time until well incorporated, then beat in the vanilla extract.
Add the flour mixture in two additions, alternating with the nut milk. Divide the batter among the prepared baking pans and spread to the edges.
Bake 20 to 25 minutes, until golden brown around the edges and the tops are just firm to the tough.
Remove and let cool in the pans 30 minutes, then run a sharp knife around the edges and flip out onto wire racks to cool completely.
Frosting and Garnish
Prepare the frosting according to the directions. Reserve about ½ to ⅔ cup of the frosting for piping decoratively.
Place one layer of cake on a cake stand or plate. Spread the top with one-third of the remaining frosting. Place the second layer on top and spread the top with another third of the frosting. Spread the sides with the final third.
Use the reserved frosting to pipe rosettes or stars around the edge of the top of the cake. Sprinkle the top with 1 tablespoon sugar free sprinkles.
To add sprinkles to the side of the cake: Set the cake plate on a clean counter. Pour sprinkles into your hand and gently press around the bottom 1 to 2 inches, letting any that don't stick fall onto the counter. Turn the cake as you press more into the bottom.