Note: 4.5 ounces flour equals just shy of 1 cup.

Preheat oven to 350 F. Spran and line 2 8 cake pans with parchment..

Cream together the butter and sugar for a few minutes until mixture is light and fluffy.

Add in the vanilla extract, then egg + yolks one at a time, creaming until mixture is smooth and fluffy again. Batter may look curdled - thats okay.

In a small bowl, stir together the cake flour, baking powder, and salt. In a measuring cup, measure out the milk and sour cream and then mix the two together.

Alternate adding the dry ingredients and milk mixture to your machine running on low-medium speed, starting and ending with the dry ingredients. Mix till just combined.

Divide batter evenly in cake pans. Bake 20 to 25 minutes, or until a toothpick inserted comes out clean or with a few crumbs.

Buttercream: Using a wire whisk attachment , whip the butter for a few minutes. Add in the confectioners sugar, salt, and vanilla extract and whip until light and fluffy. Add in milk and beat till smooth. Add more milk if frosting is too thick.

Notes: made these as cupcakes for Amys birthday 3/18. Great light fluffy cupcakes. Put sprinkles in for a funfetti version. Used chocolate ganach frosting.