Cream shortening, butter and sugar til light. add vanilla and mix well. Sift together flour, baking powder and salt. add to creamed mixture alternately with milk, beating after each addition. Gently fold in egg whites.
Turn into a greased and lightly floured 9 inch round layer cake pan and bake at 375 for 18 to 20 minutes or til cake springs back when lightly touched. Frost with favorite boiled white frosting, caramel frosting, or any desired frosting.