Add all ingredients except chocolate chips and nuts into a blender. Blend until smooth. If desired, mix in chocolate chips and nuts by hand.
Bake for 20-22 minutes, allow to fully cool on wire rack.
Notes
This recipe calls for 1 cup of pumpkin purée, which is about half a can. Since it's hard to save half a can, I typically will double the recipe, which yields roughly 24 muffins.One batch for this week, freeze the other batch for next week.