Measure sifted flour, add baking powder and 2 teaspoons salt, and sift together three times. Beat egg whites until foamy, add 1 cup white sugar gradually, and continue beating only until mixture will stand in soft peaks. Cream shortening, add 2 1/2 cups white sugar gradually, and cream together until light and fluffy. Add flour, alternately with milk, a small amount at a time, beating after each addition until smooth. Add 2 teaspoons vanilla and egg whites and beat thoroughly into batter.
Turn batter into one round 10 inch pan and one round 8 inch pan, 3 inches deep, each lined on bottom with paper, filling each pan about half full of batter. Bake in moderate oven 350 degrees F (175 degrees C), placing the smaller layer towards front of oven for quicker and easier removal when done. Bake the 8 inch cake 1 hour, or until done; bake the 10 inch cake about 10 minutes longer.
Cool cakes in pans on racks 15 minutes. Then loosen from sides of pans with spatula, turn out, remove paper, and turn right side up on racks to cool. When thoroughly cooled, at least 2 hours, brush cakes to remove any loose crumbs. Prepare Creamy Butter Frosting and set aside about 2 cups of frosting for decorating. Spread with frosting. You can tint the frosting the color or colors you want and be able to write on top of cake.
To Make Creamy Butter Frosting: Cream 1 cup butter or margarine; add part of the confectioners' sugar gradually, blending after each addition. Mix in 4 teaspoons vanilla and 1/2 teaspoon salt. Then add remaining sugar alternately with milk, until of right consistency to spread. Beat after each addition until smooth. Makes about 5 cups. (While frosting cake, keep bowl of frosting covered with a damp cloth to prevent drying.)