Preheat oven to 375 degrees and line a muffin tin with papers.
Add the cake mix, cinnamon, and pumpkin pie spice to a large bowl and whisk to combine.
Make a well in the center of the dry ingredients and add the pumpkin puree, eggs, oil, milk, and vanilla. Whisk the wet ingredients together in the well until smooth.
Gradually stir the wet and dry ingredients together, mixing just until combined, taking care not to over-mix.
Spoon batter into the muffin cups, filling each about ¾ full.
Stir together the optional sugar and cinnamon topping and sprinkle a little over each muffin.
Bake 18-22 minutes, until a toothpick inserted in the center comes out clean.
Cool the muffins in the tin a few minutes before moving to a rack to cool completely.