Preheat oven to 400° Fahrenheit (204° Celsius).
In a large mixing bowl, combine flour, baking powder, baking soda, and salt.
In a small mixing bowl, combine both sugars, sourdough starter, butter, milk, vanilla extract, and egg.
Stir together the wet ingredients into the dry ingredients until just moistened.
Fold in chocolate chips.
Lightly grease a muffin tin and spoon muffin batter into each cup, about 2/3 full.
Bake for 20 minutes. Insert a toothpick, and if it comes out clean, the muffins are done.