• Preheat the oven to 425°F. Line a 12-cup muffin pan with paper liners.
• Melt the butter in a small saucepan over low heat and then let it cool to about 85°F. (Note: If the butter starts to splatter and pop while melting, the heat is too high, reduce it further).
• Place the flour, baking powder, baking soda, and salt in a medium bowl and whisk for 30 seconds to thoroughly combine all the ingredients.
 Add the chocolate chips to the dry ingredients and toss to coat the chips with flour.
• Place the brown sugar, granulated sugar, and pumpkin pie spice in a bowl and whisk together. Use your fingers to break up the clumps of brown sugar.
• Add the eggs and whisk for 1 minute. The eggs will be thoroughly combined with the sugars, and the batter will be lighter in color. Add the cooled melted butter to the mixture and whisk it in until thoroughly combined.
• Whisk in the buttermilk and then the pumpkin puree. Let the wet ingredients sit for 10 minutes to give more time for the sugar to dissolve.
• Add half of the chocolate chip-flour mixture to the wet ingredients. Use a silicone spatula to fold the dry ingredients into the wet ingredients. Add the remaining flour mixture and fold it in until the dry ingredients are thoroughly incorporated, and no white specs of flour remain. The batter will be lumpy which is okay.
• Divide the batter between the 12 muffin cups, about 95 grams of batter for each muffin cup. The batter should almost be the top of each paper liner.
• Place the muffin pan in the oven and bake the muffins at 425°F for 5 minutes. Without opening the oven door reduce the temperature to 350°F and bake the muffins for another 15-18 minutes. The muffins will rise and have slightly craggly tops.
• Test for doneness by inserting a toothpick in the center. It should only have a few crumbs clinging to it. If it is wet batter the muffins are done. The other method is to check the temperature in the center of the muffin with an instant read thermometer. It should register 202°F.
• Remove the muffin pan from the oven and let the muffins cool in the muffin pan for 5 minutes. Place the individual muffins on a wire rack to finish cooling. The muffins can be (and should be) served warm.

Storage

• Store the pumpkin muffins in an airtight container for up to 3 days. For longer storage, wrap them individually in plastic wrap and store in the refrigerator for up to 5 days.