Preheat oven to 350. Grease two 9" layer pan; dust with flour. Cream butter and sugar together in bowl until thoroughly mixed. Add yolks and beat well.

In separate bowl, stir flour, baking powder and salt together. Alternately add flour mixture and milk to sugar mixture; beat well after each addition. Stir in vanilla.

Beat whites until stiff; fold into batter. Pour batter into pans; bake for 30 minutes. Cool in pans on wire rack for 10 minutes, then turn out onto rack; cool completely before frosting.

To make frosting, combine sugar, butter, salt, milk and juice in bowl; beat with mixer until smooth. Frost sides and top of cooled cake.

Variation: To make chocolate frosting, melt 1 ounce unsweetened baking chocolate and add to remaining ingredients.