Heat the oven to 375°. Spray the bottoms only of 12 standard-size muffin cups and set the pan aside.
Measure the flour, sugar, baking powder, salt, and nutmeg into a large mixing bowl and combine them with a whisk.
In a medium bowl, whisk the egg until it's frothy. Blend in the milk, melted butter (make sure its cooled so you don't scramble your egg), and vanilla extract.
Make a well in the dry ingredients and pour in the liquid mixture.
Using a wooden spoon, mix the batter just until it's evenly blended.
Add the chocolate chips, then spoon it into the muffin cups, filling each about two-thirds full. I like to use a cookie scoop.
Bake the muffins for 15 minutes. Then rotate the pan and bake for an additional 5 to 7 minutes.
Let cool on a wire rack for about 5 minutes before removing.