Preheat oven to 375℉.

Measure out all ingredients for quicker prep.

Melt 1 stick of butter in a large bowl in the microwave or on the stove.

Whisk in pumpkin puree, brown sugar, and granulated sugar. Add sour cream, vanilla, and eggs, whisking vigorously to incorporate.

Combine flour, cocoa powder, baking soda, baking powder, and salt in a medium bowl and mix.

Add flour mixture to the wet ingredients and mix until just combined, with no dry flour bits remaining. The batter will be thick and a little lumpy.

Gently fold in the chocolate chips.

Cover the bowl with a clean dish towel and rest the batter for 15 minutes.

Line muffin pan with 12 tulip-style parchment paper liners. Add approximately 1/4 cup of batter per liner.

Place muffin pan on the center rack. Once the oven door is closed, reduce the oven temperature to 350℉.

Bake for 25-27 minutes. Check for doneness after about 26 minutes.

Allow to cool for a few minutes in the muffin tray, then transfer to a wire rack to finish cooling.