Preheat oven to 350 degrees F (175 degrees C). Grease and flour a 9x13 inch pan.
Reserve 1 cup of cake mix from the package. In a bowl, combine remaining cake mix, 1 egg and melted margarine. Press mixture into the bottom and up the sides of a 9x13 inch pan to form a crust.
Mix together the pumpkin, 3 eggs, sugar, cinnamon and evaporated milk until blended.
Pour over the crust.
Combine the brown sugar and reserved 1 cup cake mix, then cut in the margarine until mixture is crumbly.
Sprinkle over the filling.
Bake in the preheated oven for 50 minutes. Keep refrigerated.
