Preheat the oven to 375°F (190°C)
Line a muffin tin with paper liners or grease the cups
Mix flour, sugar, baking powder, and salt in a bowl
In another bowl, whisk milk, eggs, melted butter, and vanilla
Pour the wet ingredients into the dry ingredients
Stir gently until just combined
Fold in any add-ins like berries, chocolate chips, or nuts
Divide the batter evenly among the muffin cups
Bake for 18 to 22 minutes
Check for doneness with a toothpick
Let the muffins cool in the pan for a few minutes
Transfer the muffins to a wire rack to cool completely