Preheat oven to 350 degrees F (175 degrees C). Grease and flour baking pan; 9x13 inch, or 2 round 9 inch pans.
In a large bowl, measure flour, sugar, baking powder, salt, shortening, milk and the vanilla into a large mixing bowl. Beat 2 minutes on high speed, scraping bowl occasionally.
In a large glass or metal mixing bowl, beat egg whites until stiff peaks form. Fold 1/3 of the whites into the batter, then quickly fold in remaining whites until no streaks remain.
Pour batter into pan(s), Bake 9x13 inch cake for 35 to 40 minutes. If using 9 inch rounds, bake 30 to 35 minutes. A toothpick inserted into the cake will come out clean.
