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 until well blended.
03 - In a separate bowl, whisk melted butter, oil, granulated sugar, brown sugar, eggs, buttermilk, and vanilla extract until smooth and fully incorporated.
04 - Pour wet ingredients into dry ingredients and fold gently until just combined. Small lumps are acceptable—avoid overmixing to ensure tender texture.
05 - Fold in 1 3/4 cups chocolate chips, reserving a small handful for sprinkling on tops.
06 - Divide batter evenly among muffin cups, filling each completely to the top. Sprinkle reserved chocolate chips over batter.
07 - Bake at 425°F for 5 minutes to create domed tops, then reduce temperature to 350°F and continue baking 13–15 minutes until a toothpick inserted in center comes out clean or with moist crumbs.
08 - Let muffins cool in tin for 5 minutes, then transfer to a wire rack to cool completely before serving.