Preheat oven to 375°F. Grease or line a 12-cup standard muffin pan.
In a large mixing bowl, whisk together the flour, sugar, cocoa powder, baking powder, baking soda, and salt.
Stir in chocolate chips.
In a small mixing bowl, combine the milk, butter, egg, and vanilla.
Add the milk mixture to the flour mixture and stir until just combined.
Transfer the batter to the prepared pan.
Bake 15 to 20 minutes, or until a pick inserted into the center comes out clean.
Be careful not to overmix the muffin batter as this may lead to muffins that are tough. Mix the dry ingredients and the wet ingredients separately. This will minimize the amount of mixing needed when you combine the wet ingredients with the dry.
Use a large cookie scoop to transfer the batter to the individual muffin cups. This will ensure all the muffins are the same size and will bake evenly.
Remove the muffins to a wire rack to cool. Don’t allow the muffins to cool in the pan or the bottoms of the muffins may become soggy.
Lining the muffin pan with baking cups will result in the outsides of the muffins being lighter in color and softer in texture. Greasing the pan will result in a darker and crisper texture to the outsides of the muffins.