Step 1

Preheat oven to 350 degrees. Lightly butter a 4 1/2-by-8 1/2-inch loaf pan. Whisk together flour, baking powder, baking soda, salt, cinnamon, and nutmeg. In a large bowl, using a mixer, beat butter and sugar on medium-high until light and fluffy, 7 minutes. Add eggs, one at a time, beating well after each addition and scraping down bowl as needed. Beat in vanilla. With mixer on low, gradually add flour mixture and beat until just combined. Add pumpkin and buttermilk and beat until just combined.

Step 2

Transfer batter to pan, smooth top, and bake until a toothpick inserted in center comes out with a few moist crumbs attached, about 1 hour 15 minutes (cover with foil if overbrowning). Let cool in pan on a wire rack, 15 minutes. Turn out onto rack and let cool completely. (To store, wrap in plastic and keep at room temperature, up to 3 days.)