Disregard the directions on the box of cake mix, instead beat the egg whites until stiff. Combine them with the cake mix and water and beat until thoroughly blended about 2 minutes. Pour the batter into the molds, fillng each one about 3/4 inch. Bake for about 30 minutes or until the cake is golden brown and a toothpick stuck in the center comes out clean.
For the filling cream the butter and shortening, slowly add the sugars while beating. Add the evaporated milk, vanilla and lemon extract. Mix on medium speed until completely smooth and fluffy. When the cakes are done and cooled, use a tooth pick to make three small holes in the bottom of each one. Move the toothpick around the inside of each cake to create space for the filling. Using a cake decorator or plastic bag or pastry bag inject each cake with filling through all three holes.