1-1/4 cups butter (no substitutes, softened), 1-1/2 cups sugar, 4 eggs, 2 cups (16 oz) sour cream, 1/4 cup milk, 2 T. lemon juice, 1 - 2 T. grated lemon peel, 1 T. vanilla extract, 5 cups flour, 2 t. baking powder, 2 t. baking soda, 1/4 t. salt, 1/4 cup poppy seeds.
In a large mixing bowl, cream butter and sugar. Add eggs, one at a time, beating well after each addition. Combine the sour cream, milk, lemon juice, peel and vanilla; add to creamed mixture. Combine the flour, baking powder, baking soda and salt; add to the creamed mixture and beat just until combined. Stir in poppy seeds (batter will be thick).
Transfer to three greased and floured 9" round baking pans. Bake at 350 degrees for 25 - 30 minutes. Cool for 10 minutes before removing from pans to wire racks.
Frost and assemble layers atop each with a cream cheese frosting of your choice.