Heat oven to 425 degrees. Prepare a 6-cup jumbo-size muffin tray by spraying cups with non-stick cooking spray.
In a large bowl, whisk together the flour, baking powder, baking soda and salt. Add chocolate chips and stir to evenly distribute.
In a separate bowl, combine the butter, sugar, eggs, buttermilk and vanilla. Whisk well, then slowly add to the flour mixture, stirring with a wooden spoon or rubber spatula, just until combined. Do not overmix.
Divide the batter between the 6 muffin cups, filling them all the way to the top, then bake at 425 degrees for 5 minutes. Without opening the oven door, reduce the temperature to 375 degrees and continue to bake for 25-26 minutes more, or until a toothpick inserted into the center of a muffin comes out clean. Do not overbake.
Cool for 5 minutes, then serve.