Preheat the oven to 375°F and line a 12 cup muffin pan with muffin liners. In a large bowl or stand mixer, mix together the melted butter, granulated sugar and brown sugar until smooth.A dd the eggs one at a time, mixing after each addition.
Add the pumpkin purée, sour cream and vanilla extract and mix until combined. Add the flour, baking soda, baking powder, cinnamon, pumpkin pie spice and kosher salt. Gently mix until just combined, being careful not to over mix.
Fold in 1 cup of mini chocolate chips until evenly distributed throughout the batter. Divide the batter evenly between the 12 prepared muffin cups. Generously sprinkle additional mini chocolate chips over the tops of each muffin.
Bake at 375°F for 5 minutes, then, without opening the oven door, reduce the temperature to 350°F and bake for an additional 14–16 minutes, or until a toothpick inserted into the center comes out clean or with a few moist crumbs.
Allow the muffins to cool in the pan for about 10 minutes before transferring them to a wire rack to finish cooling.