Preheat the oven to 350 degrees and grease a 9×13 inch cake pan.
Set aside 1 cup of cake mix. Add the rest of cake mix, melted butter and 1 egg and mix until well combined. Spread the mixture in the bottom of the prepared cake pan.
In a large bowl combine pumpkin, brown sugar, milk, 3 eggs, pumpkin pie spice, cinnamon and mix well. Spread this mixture over cake mix mixture.
In a small bowl combine the reserved cake, granulated sugar, and butter. Using a fork mix until the mixture resembles small crumbs. Sprinkle over the pumpkin mixture. Bake for about 50 minutes or until the top is golden. Cool to room temperature on a wire rack and refrigerate for about 4 hours or until completely chilled.
Recipe by Reality Daydream at https://realitydaydream.com/better-than-pumpkin-pie-cake/