To make pumpkin cake using two ingredients, pour a spice cake mix into a large bowl, and stir in a 15-ounce can of pumpkin pie filling. Spread the pumpkin mixture into a greased baking pan, and bake the pumpkin cake for 35 to 40 minutes.
A can of pumpkin pie filling provides enough moisture to the spice cake mix to create a batter. You can use regular canned pumpkin puree for the moisture, but it does not contain the typical pumpkin pie spices found in canned pumpkin pie filling, such as cinnamon, cloves and ginger.
Combine the cake mix and pumpkin pie filling with an electric mixer on low speed. Stir the ingredients until they combine completely. Grease the sides and bottom of the pan so the cake doesn't stick. You can use a regular 13- by 9-inch baking pan, a Bundt cake pan or a cupcake pan if making pumpkin cupcakes.
Sprinkle the cake with powdered sugar for a simple topping. Another option is to make a glaze by combining 1 1/2 cups of powdered sugar, 3 tablespoons of apple cider and 3/4 teaspoon of pumpkin pie spice. Pour the glaze over the cake while it is still warm.