Preheat oven to 425°F. Grease a 12-count muffin tin with nonstick spray or line with paper liners. If you have 2 muffin tins, prepare 4 muffin wells of a second tin. Set aside.
In a large bowl, whisk the flour, baking powder, baking soda, and salt together.
3 cups all-purpose flour, 1 tablespoon baking powder, ½ teaspoon baking soda, ½ teaspoon kosher salt
In another bowl, whisk the melted butter, oil, sugar, and eggs together. Add the buttermilk and vanilla and whisk well.
½ cup unsalted butter, ¼ cup vegetable oil, 1 cup granulated sugar, 2 large eggs, 1 cup buttermilk, 2 teaspoons pure vanilla extract
Pour the wet ingredients to the dry ingredients and mix just until combined.
Gently fold the chocolate chips into the batter.
1½ cups semisweet chocolate chips
Use a portion scoop to fill each muffin well with batter, about ⅔ full. If you are using 2 muffin tins, fill all 16 muffin wells with batter. If you are using 1 muffin tin, cover the bowl of remaining batter and set aside. Sprinkle the muffins with coarse sugar, if desired.
Coarse sugar
Bake at 425°F for 5 minutes. Keep the muffins in the oven and reduce oven temperature to 350°F. Continue to bake for 16-18 minutes or until a toothpick inserted into the center of a muffin comes out clean.
Let the muffins cool in the pan for 10 minutes, then transfer to a cooling rack. Bake the remaining muffins, serve, and enjoy.