Preheat your oven to 350°F (175°C).
Grease a mini muffin tin or line it with muffin liners.
In a large bowl, whisk together flour, sugar, and baking powder.
In another bowl, combine milk, melted butter, and egg.
Pour wet ingredients into dry ingredients and mix until just combined.
Fold in chocolate chips or fruit if using.
Fill each muffin cup about 2/3 full with batter.
Bake for 15-20 minutes or until a toothpick comes out clean.
Let cool in the pan for 5 minutes before transferring to a wire rack.
Enjoy warm or at room temperature!