Combine butter, sugar, egg yolks, and vanilla in a mixing bowl.  Cream these ingredients together thoroughly. 

Mix flour, salt, and baking powder together in a separate mixing bowl.  Add dry ingredients to creamed ingredients 1/3 at a time  alternating with adding portions of the orange juice to the creamed mixture. 

Fold in beaten egg whites.  Spoon batter into cupcake liners until 1/2 full. 

Bake in a 350 degree preheated oven for 15 minutes or until a toothpick inserted in center comes out clean.

Cool cupcakes completely before frosting with Orange Icing.