Pour cake mix into a large bowl and whisk to remove any lumps. Add pumpkin and stir until completely smooth and uniform.
Cook's Note: Do not add any other ingredients that may be mentioned on the cake mix box, like eggs, oil, or water. The mixture will be very thick, so you might be tempted to add in other things to make the batter smoother. Do not do this!
Place batter into a 12-cup muffin pan lined with foil baking cups and/or sprayed with nonstick spray. Place pan in the oven and bake until a toothpick inserted into the center of a muffin comes out clean, about 20 minutes.
Allow to cool slightly and then serve. Garnish with fresh berries, if using. Enjoy!