Preheat oven to 350 degrees F (175 degrees C) and lightly grease a 9x13 inch baking dish.
Set aside 1 cup of cake mix. Combine remaining cake mix with melted butter and 1 egg and mix until well blended; spread mixture in the bottom of the prepared baking dish.
In a large bowl combine pumpkin, brown sugar, milk, 3 eggs and pumpkin pie spice; mix well and pour this mixture over cake mix mixture in baking dish.
In a small bowl with a pastry blender, or in a food processor, combine chilled butter and white sugar with reserved cake mix until mixture resembles coarse crumbs. Sprinkle over pumpkin mixture. Sprinkle chopped walnuts over all.
Bake 45 to 50 minutes, until top is golden.
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