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 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 mixture is smooth and fully incorporated.
04 - Pour wet ingredients into dry ingredients. Fold gently using a spatula until just combined; avoid overmixing as small lumps are acceptable and ensure tender texture.
05 - Fold in chocolate chips, reserving a small handful to sprinkle on tops before baking.
06 - Divide batter evenly among muffin cups, filling each to the very top. This ensures tall bakery-style domes. Top with reserved chocolate chips.
07 - Bake at 425°F for 5 minutes to create initial rise. Reduce temperature to 350°F and continue baking for 13-15 minutes until a toothpick inserted in center comes out clean or with a few moist crumbs.
08 - Let muffins cool in the tin for 5 minutes before transferring to a wire rack. Allow to cool completely before serving.