Preheat the oven to 425°F. Melt the butter and set aside to cool.
Line a muffin pan with cupcake wrappers in every other cup.
In a large bowl, whisk together the flour, granulated sugar, brown sugar, pumpkin pie spice, baking powder, baking soda, and salt.
In a large measuring cup, whisk together the pumpkin puree, cooled melted butter, oil, milk, eggs, and vanilla.
Add the wet ingredients to the dry ingredients. Mix until just combined - don't overmix.
Gently fold in the mini chocolate chips.
Scoop batter into the prepared muffin cups, filling each to the top.
Sprinkle extra chocolate chips on top of each muffin and press gently so they stick.
Bake at 425°F for 5 minutes, then lower the temperature to 375°F and bake for an additional 16–18 minutes, or until the edges are golden and the centers are set.
Remove from the oven and let the muffins cool before serving.
Notes
Every other cup: Bake in every other muffin cup rather than filling all 12 at once - it lets heat fully surround each muffin, giving you consistently tall, domed tops.Mini chips over regular: Mini chocolate chips distribute more evenly and stay suspended in the batter, so you get chocolate in every bite instead of chips sinking to the bottom.The temperature drop matters: Starting hot at 425°F for the first 5 minutes, then dropping to 375°F, is what gives these muffins their bakery-style rise - don't skip this step or bake the whole time at one temperature.Don't overmix: Stop as soon as the flour disappears. A little bit of flour is okay, and it’ll mix in as you fold in the chips.