Preheat oven to 325°F (160°C).

Sift flour and baking powder together three times.

In a separate bowl, cream shortening and sugar until light and fluffy.

Gradually add the sifted flour mixture to the creamed mixture, alternating with milk or water.

Beat well after each addition to ensure a smooth batter.

Stir in vanilla extract.

Gently fold in the stiffly beaten egg whites until just combined.

Pour the batter into a greased and floured 9 x 13-inch baking pan.

Bake for 50 minutes, or until a wooden skewer inserted into the center comes out clean.

Let the cake cool in the pan for 10 minutes before transferring it to a wire rack to cool completely.

Frost with your favorite icing or dust with powdered sugar before serving.