In a mixing bowl, combine pumpkin puree, melted butter, granulated sugar, egg, and vanilla extract. Whisk until smooth.

In a separate bowl, whisk together flour, baking soda, baking powder, salt, and ground cinnamon. Add to wet ingredients, mixing gently.

In a small bowl, mix melted butter, brown sugar, and ground cinnamon for the swirl. Set aside.

Line muffin pan with liners, fill half with muffin batter, drizzle cinnamon swirl mixture, then top with remaining batter. Swirl with a knife.

Preheat oven to 350°F and bake muffins for 20-25 minutes until tops are golden brown.

While cooling, whisk together powdered sugar, vanilla extract, and milk for the glaze. Adjust milk for consistency.

Once cooled, remove muffins from pan and drizzle glaze over muffins.