This is the first of what I'm sure will be half a dozen follow ups to my basic white cake recipe post.
Grease your pan with margarine (or butter, I guess). Peel, core and thinly slice 3 medium apples--any kind you like. Layer half the apples on the bottom of your baking dish. Sprinkle about 1/4-1/2 cup (yeah, I don't measure...just be generous) of brown sugar over the apples. Add about 1-2 tbsp of ground cinnamon to the dry ingredients in the cake batter. You could also toss in some nutmeg or ginger or heck, even pumpkin pie spice would rock. Layer the rest of the apples on top of the cake batter, and again, sprinkle with 1/4-1/2 cup of brown sugar.
Bake as directed.