Preheat oven to 350°F and set aside a 9x13-inch baking dish.
Mix together 30 ounces pumpkin puree, 12 ounces evaporated milk, 4 large eggs, 1½ cups granulated sugar, 1 tablespoon vanilla extract, 2 teaspoon ground cinnamon, and 2 teaspoon pumpkin pie spice.
Pour the pumpkin mixture into the baking dish.
Evenly sprinkle the 1 box yellow cake mix over the top of the pumpkin puree mixture. I like to sprinkle mine with a little extra pumpkin pie spice after the cake mix has been added.
Melt 1 cup salted butter and pour it over the cake mix, or cut the butter into thin slices and evenly distribute them to cover the top of the cake.
Finally, spread the 1 cup chopped walnuts or pecans evenly over the top of the cake. Bake for 1 hour.
Serve warm with vanilla ice cream, whipped cream, and a dash of pumpkin spice.