To prepare cake:
Heat oven to 350 degrees. Grease and flour three 9-inch cake pans. Cream butter, shortening and sugar. Beat egg yolks thoroughly, and add to creamed mixture. Sift flour and baking powder together; add to creamed mixture alternately with milk. Add lemon juice and rind. Fold in stiffly beaten egg whites. Divide batter evenly into 3 cake pans. Bake in preheated oven for 30-35 minutes, or until cake tests done. Remove from oven, invert onto wire racks, remove pans, and let cool. Frost with Lemon Glaze Icing.
To prepare icing:
Combine all ingredients and boil to jelly-like consistency. Let cool slightly. Beat well. (Recipe may be doubled if thicker glaze on cake is desired.) Makes enough icing for layers and top of 3-layer cake.
SERVES: 10 - 12