Preheat the oven to 350ºF. In a stand mixer add the brown sugar, flax egg, and vegan butter. With the paddle attachment mix on low for 2 minutes.
On low speed add the molasses and mix for 30 seconds, scrape down the sides and mix for another 30 seconds.
With the mixer still on add the boiling water, mix on low for 1 minute.
Add the ginger, cinnamon, cloves, and salt. Allow it blend then add the guar gum and baking soda.
Add the flour and then increase the speed to medium and mix for 2 minutes, scraping the sides of the bowl halfway through.
Pour into a greased 8x8 baking dish. Bake 15-22 minutes or until a butter knife comes out of the center clean.
Allow it to sit and cool for about 15 minutes and then you can transfer it to a serving plate if desired. Sprinkle with powdered sugar and serve.
Notes
The powdered sugar will settle overnight, so if you plan to make the gingerbread ahead, sprinkle the powdered sugar on just right before serving. This will last about 2-3 days on the kitchen counter covered.