Poppy Seed Cake I

1 1/2 cups sugar
1/2 cup butter
4 egg yolks
2 cups flour
1 teaspoon baking soda
3/4 cup poppy seeds
1 1/4 cups sour cream
4 egg whites
1 teaspoon vanilla

Cream butter, sugar and egg yolks. Add dry ingredients alternately with sour cream. Beat egg whites and vanilla until fluffy but not stiff. Fold into creamed mixture. Pour into greased Bundt pan or two cake pans. Bake at 350 degrees for 45-60 minutes in Bundt, 30-35 in cake pans. Frost with Cream.