Preheat the oven to 375℉/190℃ and line a muffin tin with liners. Set aside.
In a bowl, add in the flour, sifted cocoa, baking soda, baking powder, pumpkin spice, cinnamon, cornstarch, and salt. Stir together and set aside.
2 cups all-purpose flour, 1/4 cup unsweetened cocoa powder, 1 tsp baking soda, 1 1/2 tsp baking powder, 2 tsp cinnamon, 1/2 tsp pumpkin spice
In another large bowl, add in the eggs, pumpkin, brown sugar, white sugar, vanilla, orange zest (optional), and sour cream. Whisk together until well combined (about 1-2 minutes).
3/4 cups dark brown sugar, 1/4 cup white sugar, 2 tsp orange zest, 2 large eggs, 1 tbsp vanilla, 2/3 cups oil, 1 1/4 cups pumpkin puree, 1/2 cup sour cream
Add in the dry ingredients and with a spatula, gently fold to make a soft muffin batter. Do not over-mix!
Add in the chocolate chips and stir in a few times. Do not over-mix!
3/4 cups semi-sweet chocolate chips
Scoop evenly between the muffin liners, filling them all the way to the top. Sprinkle extra chocolate chips and white sugar on top (optional).
Bake for 22-30 minutes. The muffins are ready when a toothpick inserted comes out clean. Allow to cool, and enjoy!