Preheat your oven to 350°F (175°C) and line a muffin tin with paper liners.
In a large bowl, whisk together the flour, sugar, baking powder, and salt.
In another bowl, combine the milk, egg, melted butter, and vanilla extract.
Pour the wet ingredients into the dry ingredients and mix until just combined.
Gently fold in blueberries or chocolate chips if using.
Spoon the batter into the prepared muffin tin, filling each cup about 2/3 full.
Bake in the preheated oven for 15-20 minutes until golden brown.
Remove from the oven and let cool in the pan for 5 minutes.
Transfer the muffins to a wire rack to cool completely.
Serve warm with your favorite toppings like syrup or whipped cream.