Step 1

Preheat oven to 350 degrees. Butter two 8 1/2-by-4 1/2-inch loaf pans. In a large bowl, whisk together flour, baking powder, baking soda, cinnamon, nutmeg, allspice, and salt.

Step 2

Combine pumpkin puree and sugars in a mixing bowl and beat with an electric mixer until combined, 2 to 3 minutes. Add eggs and melted butter and beat to combine, scraping down sides of bowl as needed. With mixer on low, add flour mixture in two batches, alternating with the buttermilk and beginning and ending with the flour; beat to combine.

Step 3

Divide batter between prepared pans; smooth tops. Bake, rotating once, until a cake tester inserted in center comes out clean, 70 to 80 minutes for large loaves, 45 minutes for small. Transfer to wire rack to cool 10 minutes. Turn out of pans, re-invert onto wire rack, and cool completely.