
Preheat oven to 300F (145C) and thoroughly grease and flour a 12 cup bundt pan or ten inch tube pan. Set aside.
Combine butter and sugar in a large bowl (or the bowl of a stand mixer fitted with the paddle attachment) and use electric mixer to beat together until thoroughly creamed.
Add egg yolks, one at a time, beating well after each addition, then stir in vanilla extract.
In a separate bowl, whisk together flour, baking soda, and table salt.
Alternate adding flour and sour cream to the sugar mixture, starting and ending with the flour mixture (I do the flour in 4 parts and the sour cream in 3).
In yet another bowl (this one medium-sized and completely clean, dry, and grease free), place egg whites and use a clean electric mixer to beat until you have stiff peaks. Fold gently into batter.
Pour batter evenly into prepared pan and transfer to 300F (145C) oven and bake for 90 minutes or until a wooden skewer inserted in the center comes out clean or with a few moist crumbs.
Allow to cool for 10 minutes before removing from pan.