Easy Crumb Cake

1 Box Yellow Cake Mix
1 cups flour
2 sticks butter
1 1/2 cups brown sugar
3 teaspoons cinnamon

Mix and bake yellow cake mix as directed, but back only for 20 minutes.  While cake is baking, mix the rest of the ingredients together until it forms large clumps.  After cake has baked for 20 minutes, sprinkle crumb mixture over cake and bake for 20 more minutes or until a toothpick inserted in center comes out clean.