Preheat oven to 375. Grease ten muffin cups.

In a large mixing bowl, stir together flour, cornmeal, sugar, baking powder, soda, and salt. Whisk to combine.

On top of that mixture, pour the butter, buttermilk, sour cream, vanilla, and two egg yolks. Stir until just combined.

In a separate bowl, beat egg whites until soft peaks form (I hope for your arm's sake, that you have electric beaters or an electric mixer). With a spatula, fold the egg whites into the rest of the batter and mix gently to combine.

Fill the muffin tins so that the batter nearly reaches the top of each tin.

Bake for 25 minutes or until a toothpick comes out cleanly. The muffins will have a fairly flat top.