Start by heating your oven to 350°F (175°C).

In a mixing bowl, combine the flour with the baking soda, salt, cinnamon, and nutmeg. Give everything a good stir so the spices blend evenly.

Add the pumpkin purée, brown sugar, buttermilk, egg, and butter. Mix until the batter comes together and looks smooth.

Pour the mixture into a 9×5-inch loaf pan and level the surface.

Bake for about an hour, or until a toothpick pushed into the center comes out clean.