Pumpkin Surprise

1 box yellow cake mix (without pudding)
2 C chopped walnuts
2 sticks (1 C) melted butter
4 eggs slightly beaten
1 large can (29 oz) of pumpkin puree
1 C brown sugar
1 can evaporated milk (12oz)
3 1/2 tsp pumpkin pie spice

Preheat oven to 350 degrees. Mix and beat all ingredients except the cake mix, walnuts, and butter. Pour into 9 x 13-inch greased pan. Mix cake mix with the walnuts. Sprinkle this mix evenly on top of the mix already in the pan. Drizzle the melted butter on top of this mix. Bake 60 to 75 minutes, or until knife inserted in center comes out clean. Serve warm or cold topped with whip cream or ice cream. Serves 12 to 16.