01 - Preheat oven to 350°F. Grease 24-cup mini muffin tin with cooking spray or line with paper liners.
02 - In a large mixing bowl, whisk together flour, sugar, baking powder, baking soda, salt, and cinnamon until well blended.
03 - In a separate bowl, whisk milk, vegetable oil, egg, and vanilla extract until smooth and fully incorporated.
04 - Pour wet ingredients into dry ingredients. Fold gently with a spatula until just combined—small lumps are acceptable. Do not overmix.
05 - Divide batter evenly among prepared muffin cups, filling each approximately ¾ full.
06 - Bake for 10 to 12 minutes, or until a toothpick inserted into the center comes out clean.
07 - Let muffins cool in the pan for 5 minutes, then carefully transfer to a wire cooling rack.
08 - While still warm, dip the top of each muffin in melted butter, then immediately roll in cinnamon sugar mixture to coat thoroughly.
09 - Serve warm or allow to cool completely to room temperature before serving.