In a large mixing bowl, combine the flour, brown sugar, baking powder, cinnamon, nutmeg, and salt. In a separate bowl, whisk together the milk, egg, vegetable oil or applesauce, and pumpkin butter. Fold the wet ingredients into the dry ingredients, just until combined. Fill the muffin tins with batter, about 2 tablespoons each. Bake for 15-20 minutes, until a toothpick insered into one of the muffins comes out clean.