Preheat oven to 350°F (175°C). Grease a 9x13 inch baking dish.
In a large bowl, mix together the pumpkin, evaporated milk, eggs, sugar, cinnamon, salt, ginger, and cloves until well blended.
Pour the pumpkin mixture into the prepared dish.
Sprinkle the dry cake mix evenly over the top of the pumpkin filling.
Drizzle melted butter over the cake mix layer.
Sprinkle chopped walnuts on top, if using.
Bake for 50 to 60 minutes or until the top is golden brown and a knife inserted near the center comes out clean.
Cool completely before cutting into squares. Refrigerate leftovers.