01 - Preheat oven to 425°F. Line a 12-cup muffin tin with paper liners or grease lightly.
02 - In a large bowl, whisk together flour, baking powder, baking soda, and salt 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. Fold gently with a spatula until just combined. Stop mixing when a few lumps remain to prevent tough muffins.
05 - Fold in 1 3/4 cups chocolate chips, reserving a small handful for sprinkling on top.
06 - Divide batter evenly among muffin cups, filling each to the very top. Sprinkle reserved chocolate chips over batter.
07 - Bake at 425°F for 5 minutes to create tall domed tops, then reduce temperature to 350°F and continue baking 13-15 minutes until toothpick inserted in center comes out clean or with a few moist crumbs.
08 - Let muffins cool in tin for 5 minutes, then transfer to wire rack to cool completely before serving.