Preheat your oven to 350°F (175°C) and grease a mini muffin tin or line it with mini muffin liners.
In a large mixing bowl, whisk together the flour, baking powder, salt, and sugar until well combined.
In a separate bowl, mix the milk, egg, melted butter, and vanilla extract until smooth.
Pour the wet ingredients into the dry ingredients and stir until just combined. Be careful not to overmix; a few lumps are okay.
If using, gently fold in the mini chocolate chips.
Spoon the batter into the prepared mini muffin tin, filling each cup about 2/3 full.
Bake for 12-15 minutes, or until a toothpick inserted into the center comes out clean.
Allow the muffins to cool in the tin for 5 minutes before transferring them to a wire rack to cool completely.