Preheat your oven to 350°F (175°C) and line a muffin tin with liners.
In a large bowl, whisk together flour, baking powder, sugar, and salt.
In a separate bowl, combine milk, egg, melted butter, and vanilla extract.
Pour the wet ingredients into the dry ingredients and stir until just combined.
Fold in optional add-ins like chocolate chips or berries if desired.
Spoon the batter evenly into the prepared muffin tin, filling each cup about 2/3 full.
Bake in the preheated oven for 15-20 minutes or until a toothpick inserted comes out clean.
Once baked, remove from the oven and let cool for a few minutes.
Carefully transfer the muffins to a wire rack to cool completely.
Enjoy warm, or store for later!