Sift together flour, baking powder, salt, and sugar. Add shortening, ½ cup milk, and unbeaten eggs, and stir lightly until flour mixture is dampened. Beat vigorously with mixing spoon or in an electric mixer at medium speed for 1 minute. Add remaining milk and vanilla or grated orange rind, and beat for 2 minutes. Pour into 2 greased cake pans. Bake in moderate oven (350 degree F) for 30 minutes, or until top of cake is brown and springs back to the touch. Cool pans on cake rack.