01 - Preheat the oven to 350°F and grease a 24-cup mini muffin tin or line with paper liners.
02 - In a large bowl, whisk together the flour, sugar, baking powder, baking soda, salt, and cinnamon until well blended.
03 - In a separate bowl, whisk together the milk, vegetable oil, egg, and vanilla extract until smooth.
04 - Pour the wet ingredients into the dry ingredients and mix gently until just combined. Do not overmix to ensure tender muffins.
05 - Divide the batter evenly among the muffin cups, filling each about ¾ full.
06 - Bake for 10 to 12 minutes, or until a toothpick inserted into the center comes out clean.
07 - Allow the muffins to cool in the pan for 5 minutes, then transfer to a wire rack.
08 - While muffins are still warm, dip the tops in melted butter, then roll in the cinnamon sugar mixture to coat evenly.
09 - Serve warm or at room temperature.