Preheat the oven to 218°C. Line or grease every other cup of a 12-cup muffin tin (recipe makes 6 muffins; using every other cup creates better air flow and taller muffins).

In a medium bowl, whisk together dry ingredients: flour, baking soda, baking powder, cinnamon, mixed spice, and salt. Set aside.

In a large bowl, whisk together wet ingredients: melted butter, pumpkin puree, brown sugar, egg, and vanilla extract until smooth.

Add the dry ingredients to the bowl with the wet and stir together until a batter forms. Stir until just incorporated; do not overmix. Optional: Let batter sit at room temperature for 15-20 minutes before scooping for tallest muffins.

Spoon the batter equally into the 6 muffin cups. Top each with a generous sprinkle of granulated sugar.

Bake for 5 minutes at 218°C, then decrease the oven temperature to 180°C WITHOUT opening the oven door, and bake for 12-15 more minutes until domed and set. A toothpick inserted in the center should come out clean or with just a couple crumbs attached.

Let cool for a few minutes and enjoy!