Preheat oven to 425ºF. Grease a 12-cup muffin tin with non-stick cooking spray.
pour the milk and vinegar. Let sit while preparing the remaining ingredients.
mix together the flour, baking powder, baking soda, salt and sugar.
Add the butter, eggs, vanilla, and the milk and vinegar mixture. Stir JUST until a batter with lumps forms. Fold in the chocolate chips.
Fill each cup in the muffin tin to be completely full (about a 1/4 cup).
Bake at 425ºF for 5 minutes. Then decrease the heat to 375ºF and bake for another 13 minutes. Remove from oven and let cool for a few minutes before removing from the tin and serving.