Beat together:

2 cups + 2 T. sugar
6 oz. butter

Add:

3 yolks (save whites for later)
2 1/4 tsp. vanilla

Sift and alternately add, the following dry ingredients with the sour cream,  beginning and ending with flour:

4 3/4 cups sifted cake flour (1 lb.)
1 1/8 tsp. baking soda
3/4 tsp. salt

With 1 lb. 2 oz. sour cream

Fold in beaten egg whites (stiff but not dry), with pinch of cream of tartar.

Pour into greased and floured sheet pan, lined with parchment paper if not serving in pan.

Bake at 350 for 25 minutes or until cake pulls away at edges and center tests clean.