Crumble topping:
3/4 cup all-purpose flour
1/2 cup dark brown sugar
1/2 teaspoon ground cinnamon
6 tablespoons butter, melted but not hot

Optional:
1/2 cup of your choice - coarsely chopped nuts (walnuts, pecans, almonds), old-fashioned oatmeal or sweetened flaked coconut

Optional cream cheese filling:
8 ounces softened cream cheese
1/2 cup sugar
1 egg
1 teaspoon vanilla extract

Coffeecake batter:
1 1/2 cups all-purpose bleached flour
1 1/4 teaspoons baking powder
1/4 teaspoon baking soda
1/4 teaspoon salt
5 tablespoons butter, at room temperature
1/2 cup sugar
1 egg
1/4 cup plain low-fat yogurt

Optional fruit (or chocolate) filling:
1/2 cup of your choice - raspberry or strawberry jam; peach, cherry, or pineapple preserves; apple butter; orange marmalade or mini chocolate chips