Preheat oven to 425°F (218°C). Line a 12-cup muffin tin with paper liners or grease well. Place rack in
the middle position.
In a large bowl, whisk together pumpkin puree, granulated sugar, brown sugar, and oil until smooth.
Add eggs one at a time, then add vanilla and sour cream. Whisk until combined.
Add flour, baking powder, baking soda, pumpkin pie spice, and salt. Fold with a rubber spatula until
just combined — do not overmix.
Toss chocolate chips in 1 tsp flour, then fold into the batter with 3–4 strokes.
Divide batter evenly among the 12 muffin cups, filling to the rim. Press extra chocolate chips onto each
top.
Bake at 425°F for 5 minutes. Without opening the oven, reduce to 350°F (177°C) and bake 17–20
minutes more. A toothpick should come out with a few moist crumbs.
Cool in pan 5 minutes, then transfer to a wire rack.