Place shortening in large bowl of an electric mixer and beat 1 minute at medium speed. Scrape down the sides and bottom of bowl. Add 3 3/4 cups of splenda/sugar blend, 3/4 cup at a time, beating 1 minute after each addition.
Add about 2 cups of the dry ingredients to the shortening mixture and beat 30 seconds on medium speed. If you have a heavy-duty, large-capacity mixer, continue adding and beating, 1 cup at a time, until all ingredients are incorporated. If not, scrape the shortening mixture into the remaining dry ingredients and blend by hand with a pastry cutter or two knives until it resembles cornmeal.
Divide into 6 equal packages (each should be about 3- 1 / 2 cups when spooned lightly into a measure). Place in plastic food-storage bags, pushing out air before sealing tightly. Keep in freezer. Allow to come to room temperature before mixing.
Place 1 package of mix in bowl.
For YELLOW CAKE: Add 3 eggs, 3 / 4 cup milk, 1 teaspoon pure vanilla extract and any optional ingredients (see below). Beat 1 minute at low speed; increase to medium speed and beat 2 minutes, until batter is smooth. (Skim milk and egg substitute may be used.)
For 1 WHITE CAKE: Use 4 egg whites in place of the whole eggs, and 1 teaspoon pure vanilla extract
For 1 SPICE CAKE: Add 1 teaspoon cinnamon, 1 / 2 teaspoon nutmeg, 1 teaspoon pure vanilla extract and 1 / 4 teaspoon ground cloves. For CARROT CAKE: Add 3 cups of shredded carrots with the above ingredients
For 1 CITRUS FLAVORED CAKE: Replace vanilla with 1 / 2 teaspoon orange or lemon extract and add 1 teaspoon grated zest.
For 1 CHOCOLATE CAKE: Add 2 extra tablespoons milk, 1 teaspoon pure vanilla extract and 2 squares melted sweet or semi-sweet chocolate.
Grease and flour 2 (8-inch) round layer pans, 1 (9-by-13-inch) sheet pan or Bundt pan or 24 cupcake cups. Add batter and bake in a preheated 350-degree oven for 28 to 30 minutes for cupcakes, 30 to 35 minutes for rounds, 35 to 40 minutes for sheet cake, 40 to 45 minutes for Bundt pan.