Preheat oven to 350°F.
Heat 8 tbsp butter in a large sauté pan over medium-high heat. Cook until butter begins to brown, about 5 minutes, and remove from heat.
Add the brown sugar, vanilla, 2 tsp cinnamon, cloves, nutmeg, and ginger. Then whisk in your pumpkin puree, sour cream, and egg until fully combined.
Sift your flour, baking powder, baking soda, and salt in a fine-mesh strainer over your pumpkin puree mixture. Mix into the batter with a spatula until no flour streaks remain.
Line a 6-cup jumbo muffin tin with 6 square pieces of parchment paper. Weigh them down with something thin and heavy if they won't stay.
Remove objects from cups and, using an ice cream scooper, divide batter amongst each of the 6 muffin cups, filling most of the way in each.
In a small bowl, mix together the demerara sugar and 1/2 tsp ground cinnamon. Sprinkle generously over each muffin, dividing evenly.
Bake for 35 - 40 minutes, or until muffin tops spring back lightly when touched. Remove from oven and let cool in muffin tin.
Remove paper wrappers and slice muffins in half. Toast in a pan with 1 tbsp butter for each muffin, then top with cinnamon sugar.