Preheat your oven to 350°F (175°C) and prepare a muffin tin with liners.
In a large bowl, whisk together flour, sugar, baking powder, cinnamon, and salt.
In another bowl, combine milk, eggs, melted butter, and vanilla extract.
Fold the wet ingredients into the dry mixture until just combined.
In a small bowl, mix brown sugar with additional cinnamon for filling.
Spoon half of the batter into muffin cups, sprinkle with cinnamon filling, and top with remaining batter.
Bake for 18-20 minutes until golden brown.
