tutorial, starts with inch squares. so Easy. I have used this method many times. Starting with two 4 inch squares you end up with a 3 inch nine patch. Start with two 7 inch squares to end with a 6 inch nine patch.
See the "Rhubarb Upside-Down Cake " in our Martha Stewart's Favorite Dessert Recipes gallery. This beautiful cake has a crumb "topping" that actually ends up on the bottom. Each bite has a surprisingly crunchy texture.