01 - Preheat oven to 425°F. Line a 12-cup muffin tin with paper liners or lightly grease with cooking spray.
02 - In a large mixing bowl, whisk together all-purpose flour, baking powder, baking soda, and salt until well blended.
03 - In a separate bowl, whisk melted butter, vegetable oil, granulated sugar, brown sugar, eggs, buttermilk, and vanilla extract until smooth and fully incorporated.
04 - Pour wet mixture into dry ingredients. Fold gently with a spatula until just combined—stop when a few lumps remain. Do not overmix.
05 - Fold in chocolate chips, reserving a small handful for sprinkling on top.
06 - Divide batter evenly among prepared muffin cups, filling each to the very top. Sprinkle reserved chocolate chips over each muffin.
07 - Bake at 425°F for 5 minutes to create tall tops. Reduce temperature to 350°F and continue baking 13–15 minutes until a toothpick inserted into center comes out clean or with moist crumbs.
08 - Let muffins cool in tin for 5 minutes. Transfer to wire rack and cool completely before serving.