01 - 
                Preheat your oven to 375°F (190°C) and line a muffin tin with paper liners.
              
              
              
                02 - 
                In a large bowl, combine the flour, granulated sugar, baking powder, and salt.
              
              
              
                03 - 
                In a separate bowl, whisk together the milk, melted butter, egg, and vanilla extract.
              
              
              
                04 - 
                Pour the wet ingredients into the dry ingredients and stir just until combined.
              
              
              
                05 - 
                In a smaller bowl, mix together the brown sugar and cinnamon.
              
              
              
                06 - 
                Fill each muffin cup halfway with the batter, then sprinkle with the cinnamon-sugar mixture.
              
              
              
                07 - 
                Add the remaining batter on top, filling each muffin cup about 3/4 full.
              
              
              
                08 - 
                Swirl the remaining cinnamon-sugar mixture into the tops of each muffin with a toothpick or knife.
              
              
              
                09 - 
                Bake for 18-20 minutes or until a toothpick inserted into the center comes out clean.
              
              
              
                10 - 
                Allow the muffins to cool in the pan for 5 minutes before transferring to a wire rack.
              
              
              
                11 - 
                While the muffins cool, prepare the glaze by combining the powdered sugar, milk, and vanilla extract.
              
              
              
                12 - 
                Drizzle the glaze over the cooled muffins and serve.