Preheat the oven to 425°F. Spray a 12-cup muffin tray with non-stick cooking spray.
In a large bowl, combine the flour, baking powder, baking soda, salt and chocolate chips. Set aside.
In a medium bowl, whisk together the melted butter, sugar, eggs, buttermilk and vanilla.
Slowly add the wet ingredients to the dry ingredients. Gently fold together until just combined. Do not overmix the batter.
Divide the batter among the 12 muffin cups.
Bake at 425°F for 5 minutes. Then reduce the oven temperature to 375°F and continue to bake for another 12 to 15 minutes, or until a toothpick inserted into the center comes out clean. Do not overbake, or the muffins will be dry.
Let cool for 5 to 10 minutes.