Preheat the oven to 425°F. Fill a muffin tin with 12 paper liners.
In a large mixing bowl, sift together the flour, baking powder, salt, and baking soda.
In a medium bowl, combine the melted butter, olive oil, pumpkin puree, buttermilk, molasses, cinnamon, and nutmeg.
In the bowl of a standing mixer fitted with a wire whip attachment, beat the eggs until they are a smooth yellow color. Add the sugar and beat on medium-low speed for 1 minute, then on high for 4 minutes until the mixture forms thick ribbons.
Fold the flour mixture into the eggs; using a circular motion to completely incorporate it into the batter. Gently stir the pumpkin mixture into the batter. (Be sure to scrape the sides and bottom of the bowl as you go.) Fold in the chocolate chips.
Spoon the batter evenly into the cups, filling to the rim.
Place the muffins in the oven and lower the temperature to 375°F. Bake for 21 to 23 minutes, until a toothpick comes away clean when inserted in the center of the muffins.
Let cool in the pan for 15 minutes then lift the muffins out and let cool completely. The muffins can be stored in an airtight container for up to 3 days.