Preheat oven to 350° F. Prepare a 9.5"x5" loaf pan by lightly coating with cooking spray.
In a stand mixer or mixing bowl, combine melted butter, brown sugar and sugar until combined. Add eggs and vanilla, stir until combined. Mix in pumpkin puree.
Add gluten free flour blend, guar gum (omit if in blend), baking soda, baking powder, salt, cinnamon, ginger, cloves, nutmeg and allspice. Stir until just combined. The mixture will be dense. Pour into prepare loaf pan.
Bake for 60-65 minutes. Check for doneness by inserting a toothpick and removing the loaf from the oven when the toothpick is dry. Allow to cool for 10 minutes before removing from pan.
Store any leftovers in an airtight container or gallon baggie.