In a mixing bowl, whisk together the flour, sugar, baking powder, baking soda, and salt.
In another bowl, mix the milk, egg, and melted butter. Pour the wet ingredients into the dry ingredients and stir until just combined.
In a small bowl, mix the melted butter, brown sugar, and cinnamon for the swirl.
Heat a frying pan over medium heat and grease it lightly. Pour 1/4 cup of batter onto the pan. Swirl a spoonful of the cinnamon mixture onto the pancake.
Cook until bubbles form on the surface, then flip and cook until golden brown. Repeat with remaining batter and cinnamon mixture.
Notes:
Serve with a drizzle of icing or maple syrup for extra sweetness.