Preheat the oven to 350°F (175°C). Prepare a 12-cup muffin tin by greasing it or lining it with paper liners.
Make a large bowl by mixing together flour, cocoa powder, pumpkin pie spice, baking soda, and baking powder. Make sure everything is well combined before adding brown sugar.
Assembly
Use a spoon to make a well in the center of the dry ingredients. Pour pumpkin puree into a bowl and add eggs, vegetable oil, sour cream, and vanilla extract. Blend batter until just combined. Combine 3/4 cup chocolate chips with the batter.
Make 12 muffins by dividing the batter evenly between them. The remaining 1/4 cup of chocolate chips can be sprinkled on top.
Baking
Bake for 18 to 22 minutes, until the tops spring back when lightly pressed.
Allow cooling for 5 minutes in the tin. After cooling, transfer to a wire rack to finish cooling.
