Preheat oven to 350°F. Spray 2 (9-inch) round cake pans with baking spray with flour.

In a large bowl, whisk together flour, baking powder, salt, and baking soda.

In the bowl of a stand mixer fitted with the paddle attachment, add melted butter. Add sugars, and beat until thoroughly combined. Add eggs, milk, sour cream, and vanilla, and beat until combined. Gradually add flour mixture to butter mixture, beating until no lumps remain. (Batter will be thick.) Using a rubber spatula, fold in sprinkles. Divide batter between prepared pans.

Bake until a wooden pick inserted in center comes out clean, about 30 minutes. Let cool in pans for 10 minutes. Remove from pans, and let cool completely on wire racks. Spread Buttercream between layers and on top and sides of cake. Garnish sides of cake with sprinkles, if desired.