Leftover Oatmeal Cake with Crunchy Topping

 8 tablespoons (1 stick) butter                          1 teaspoon cinnamon
3/4 cup brown sugar                                         1/2 teaspoon baking powder
1/2 cup sugar                                                    1/2 teaspoon baking soda
2 eggs                                                               1/2 teaspoon salt
1 teaspoon vanilla                                             1 cup cooked oatmeal 
1 1/2 cups all-purpose flour

Crunchy topping:
4 tablespoons butter                                       1/2 cup oats
1/3 cup evaporated milk                                 1/2 cup unsweetened coconut flakes
1/2 cup brown sugar                                       1/2 cup chopped walnuts 
 1. Preheat oven to 350F. Grease a 9x13-inch pan or. Beat butter until fluffy. Add sugars, then eggs and vanilla, beat well. Add the dry ingredients and beat well. Stir in the cooked oatmeal.
2. Spread batter into pan.  Bake about 35 minutes. Remove cake from oven. Increase heat to broiler. 
3. Melt butter in saucepan. Stir in sugar and milk, stir until dissolved. Add oats, coconut and nuts, stir well. Spread over warm cake. Place under broiler and broil until browned and bubbly, about 4 minutes.