Preheat oven to 350 degrees F.  Grease and flour two 8-inch or two 9-inch cake pans.  Line the pan’s bottoms with parchment paper for easy release. Set aside.

In a large bowl, mix the dry ingredients together (cake flour, granulated sugar, baking powder and salt). Add the unsalted butter and blend into a paste-like consistency.

Beat the egg whites in and then whole egg, being sure to beat well after each addition.  This creates the cake’s structure. Be sure to scrape down the sides and bottom of the bowl each time.

In a small bowl, whisk the sour cream, water, vanilla, and extract together.  In thirds, pour this sour cream mixture into the egg mixture.  Beat well after each third.  Continue adding sour cream mixture until fully added and batter is fluffy, about 2 minutes.  Pour into prepared cake pans.

Bake for 30-35 minutes or until a toothpick inserted in the center of each cake comes out clean.  Cool on a wire rack for about 5 minutes, and remove from pan to cool completely.  Enjoy frosted, filled or simply alongside fresh fruit.