10 tablespoons unsalted butter, room temperature, plus more for pan
3 cups all-purpose flour, plus more for pan
2 and 1/2 teaspoons baking powder
1/4 teaspoon baking soda
1 teaspoon salt
1/2 teaspoon ground nutmeg
1/4 teaspoon ground allspice
1/3 cup buttermilk
1 and 1/4 cups pure pumpkin puree
3/4 cup light-brown sugar
2 large eggs
3/4 cup granulated sugar
2 and 1/2 teaspoons ground cinnamon
1/4 cup (1/2 stick) unsalted butter, melted
Preheat oven to 350 degrees. Butter and flour 12 standard muffin cups. Make batter: In a medium bowl, whisk together four, baking powder, baking soda, salt, nutmeg, and allspice. In a small bowl, whisk together buttermilk and pumpkin puree. In a large bowl, using an electric mixer, beat butter and brown sugar until light and fluffy. Beat in eggs, one at a time, scraping down bowl as needed. With mixer on low, add flour mixture in three additions, alternating with two additions pumpkin mixture, and beat to combine.
Spoon (an ice-cream scoop works perfectly for this) 1/3 cup batter into each muffin cup and bake until toothpick inserted in center of a muffin comes out clean, 30 minutes. Meanwhile, in a medium bowl, combine granulated sugar and cinnamon. Let muffins cool 10 minutes in pan on a wire rack. Working with one at a time, remove muffins from pan, brush all over with butter, then toss to coat in sugar mixture. Let muffins cool completely on a wire rack.