Preheat the oven – Set to 375°F (190°C) and line a muffin tin with paper liners.
Mix the dry ingredients – In a large bowl, whisk together flour, granulated sugar, brown sugar, baking powder, and salt until evenly combined.
Combine wet ingredients – In a separate bowl, whisk melted butter, milk, egg, and vanilla until smooth.
Bring it together – Pour the wet mixture into the dry ingredients. Stir gently until just combined—do not overmix.
Fill the muffin tin – Divide the batter evenly among the muffin cups, filling each about ¾ full.
Top with cinnamon sugar – Generously sprinkle the cinnamon sugar mixture over each muffin
Bake – Place on the center rack and bake for 18–20 minutes, or until a toothpick inserted in the center comes out clean
Cool & enjoy – Let muffins rest in the pan for 5 minutes before transferring to a wire rack. Serve warm or at room temperature.
