Preheat oven to 375 degrees F. Line a standard-size muffin tin with paper liners or spray with non-stick cooking spray.
In a medium bowl, whisk together the flour, ½ cup of the sugar, baking powder and salt; set aside.
In a large bowl, whisk together the melted butter and the egg. Add the milk and vanilla extract and whisk to combine.
Add one-third of the flour mixture and whisk until combined, then add another third and whisk until combined. Using a rubber spatula, fold the remaining flour into the mixture, then fold in the chocolate chips.
Divide the batter evenly between the muffin cups and sprinkle the tops with the remaining 2 tablespoons sugar. Bake until golden brown and a thin knife inserted into the center comes out clean, 15 to 20 minutes.
Remove from the oven, place the pan on a wire rack and allow the muffins to cool completely before removing. The muffins can be stored in an airtight container at room temperature for up to 4 days. (You can also freeze them by removing the paper liners, wrapping individually in plastic wrap and placing in a ziploc freezer bag.)