01 - Preheat oven to 425°F. Line a 12-cup muffin tin with paper liners or grease lightly.
02 - Whisk together flour, baking powder, baking soda, and salt in a large bowl.
03 - Whisk melted butter, oil, granulated sugar, brown sugar, eggs, buttermilk, and vanilla extract in a separate bowl until smooth.
04 - Pour wet ingredients into dry ingredients. Mix gently until just combined. Do not overmix; small lumps are acceptable.
05 - Fold in chocolate chips, reserving a small handful for topping.
06 - Divide batter evenly among muffin cups, filling each completely to the top. Sprinkle reserved chocolate chips on top.
07 - Bake at 425°F for 5 minutes. Reduce temperature to 350°F and continue baking for 13-15 minutes until a toothpick inserted in center comes out clean or with moist crumbs.
08 - Let cool in tin for 5 minutes, then transfer to wire rack to cool completely.