Make and bake cake as directed on box.Use 2 round pans for cake not 9x13.Meanwhile,warm cream cheese to room temperature.
Put cream cheese into large mixing bowl and beat it with a mixer til blended and creamy.Add can of lemon pie filling.Blend well.Fold in 1/2 the cool whip.Gently blend well.When cake is cool enough, put in freezer for a while.This makes it easier to work with.
Remove almost frozen cakes from freezer.Wrap dental floss,fishing line or some other sturdy string around the layers and pull thru the middle making 4 layers.Using pastry brush,brush away loose crumbs.
Put a small dab of lemon mix on plate to hold in place.Put 1 layer,cut side down on plate.Frost top with lemon mix.Add 2nd layer,cut side down.Add lemon mix.Repeat all 4 the same way.Any extra lemon can be put on sides to fill in gaps.Use remaining cool whip to frost top and sides of cake.Sprinkle with some decorative yellow sugar or a couple of lemon slices.Refrigerate until ready to serve.
Can be made with white cake and other flavored pie fillings if lemon isn't for you.My daughters prefer raspberry and strawberry.