Preheat the oven to 425ºF (220ºC). Spray a 12-cup muffin pan with nonstick baking spray or line with cupcake liners. You can also use a jumbo 6-count muffin pan.
Whisk the flour, baking powder, baking soda, and salt together in a large bowl until combined. Add the chocolate chips and mix to coat with the flour mixture.
In a mixing bowl, combine melted butter, oil, sugar, buttermilk, vinegar, and vanilla.
Fold the wet ingredients into the dry ingredients and mix everything together by hand. Do not overmix; the batter will be thick and a little lumpy.
Fill the muffin cups right to the top. Optional: sprinkle the tops with coarse sugar.
Bake for 5 minutes, then reduce the oven temperature to 350ºF (180ºC) and continue baking until golden brown and a toothpick inserted in the center comes out clean, another 20 to 23 minutes. NOTE: for jumbo muffins (no regular), bake for 25 - 30 minutes, until domed and golden brown.
Allow the muffins to cool for 10 minutes in the muffin pan, then transfer to a wire rack to continue cooling.