Preheat your oven to 350°F (175°C) and prepare a muffin tin by greasing it or lining it with muffin liners.

In a large mixing bowl, combine 1 cup of canned pumpkin puree, ½ cup of melted butter, ¾ cup of granulated sugar, 1 large egg, and 1 teaspoon of vanilla extract. Whisk until smooth.

In a separate bowl, whisk together 1 ½ cups of all-purpose flour, 1 teaspoon of baking soda, 1 teaspoon of baking powder, ½ teaspoon of salt, and 2 teaspoons of ground cinnamon.

Gently fold the dry ingredients into the wet mixture until just combined to avoid overmixing.

Prepare the cinnamon swirl mixture by combining 2 tablespoons of melted butter, ¼ cup of brown sugar, and 1 tablespoon of ground cinnamon. Stir well.

Spoon the batter into the prepared muffin tin, filling each cup halfway, adding a dollop of the cinnamon swirl in the center, then cover with more batter.

Bake for 20-25 minutes until golden brown and a toothpick inserted comes out clean.

Cool muffins in the tin for 5 minutes before transferring to a wire rack. Prepare the glaze by mixing powdered sugar with milk to desired consistency and drizzle over the cooled muffins.