"This recipe uses half butter and half margarine. I've discovered that although butter gives better flavor, using part margarine makes the cake moister. The fat in the margarine is softer at room temperature than the fat in the butter and this makes for a moister cake. Just be sure that you use real margarine and not something that says vegetable oil spread."
Mix flour, baking powder, and salt together; set aside. Cream butter, margarine, and sugar together until fluffy. Add egg yolks one at a time beating each one in thoroughly before adding the next one. Stir in the vanilla. Add one third of the flour mixture and mix until blended. Stir in half the milk . Add half of the remaining flour mixture and mix. Stir in remaining milk. Add remaining flour mixture and mix until batter is smooth.
Pour into two prepared 8 or 9 inch cake pans. Make sure the pans are no more than 2/3 full. Use any leftover batter for cupcakes. Bake for about 30 minutes or until the top of the cake springs back when lightly touched. Cool cakes about 15 minutes before turning out onto a cooling rack.