Preheat the oven to 375°F. Grease a 12-cup muffin pan, or line the pan with papers, and grease the papers., Whisk together the eggs, molasses, and pumpkin purée. Set aside., Whisk together the gluten-free flour or brown rice flour blend, sugar, baking powder, xanthan gum, salt, and pumpkin pie spice., Add the soft butter, mixing with an electric mixer until evenly crumbly. The mixture will look like coarse sand., Add the egg mixture a bit at a time, beating well with an electric mixer after each addition. Beat for 1 to 2 minutes, until the mixture is fluffy., Scoop the batter into the prepared pan, mounding the cups full. The batter will rise above the level of each cup; that's fine., Let the muffins rest for 10 minutes., Bake the muffins for 22 to 25 minutes, until the middle springs back when lightly touched. Remove from the oven and let rest for 5 minutes before removing from the pan. Best served warm.