Preheat oven to 375° and grease a 12 cup muffin tin. In a small bowl mix together all topping ingredients until crumbly. Set aside. In a bowl, stir together flour, baking powder, salt, and cinnamon.
In another bowl, beat together peanut butter, butter or margarine, and brown sugar until light and fluffy. Add egg and beat well. Add flour mixture and milk alternately, mixing well after each addition. Spoon batter into muffin tin, filling each cup 1/2 full. Sprinkle each with some of the topping mixture and bake at 375° F for 20-25 minutes or until a toothpick inserted into the center of a cupcake comes out clean. Cool completely and serve.
Purdue University Cooperative Extension Service