Preheat oven to 400 F. Paper-line or grease 14 muffin tin cups.
In a large bowl, mix together pumpkin, sugars, eggs, oil, and buttermilk until well-combined.
1 cup pumpkin puree, ½ cup granulated sugar, ½ cup brown sugar, 2 large eggs, ¼ cup neutral oil, ¼ cup buttermilk
Whisk in flour, pumpkin pie spice, baking soda, and salt just until combined. Don't overmix.
1 ½ cups all-purpose flour, 1 tablespoon pumpkin pie spice, 1 teaspoon baking soda, ½ teaspoon salt
Add mini chocolate chips, and stir until just incorporated.
½ cup mini chocolate chips
Divide batter evenly among the muffin cups.
Bake for 7 minutes.
Reduce heat to 375F.
Continue baking for 13-18 minutes, or until wooden pick inserted in centers comes out clean. A little melted chocolate is ok, but you don't want wet batter coming out on the toothpick.
Cool in pans for 5-10 minutes, and then remove to wire racks to finish cooling.
Notes
Oil: Neutral oils such as vegetable, olive oil, or canola will work well.
Buttermilk: Regular buttermilk or low-fat buttermilk will work.