Preheat oven to 350 degrees.
Grease the bottom and sides of a 9"x13" glass baking dish. Line with parchment paper so the parchment overhangs the long sides of the dish.
Whisk the flour, xanthan gum and salt together in a medium mixing bowl.
Add the sugars to the chocolate mixture and stir until combined. Carefully remove the double boiler insert and pour the mixture into a large mixing bowl.
Whisk the 5 eggs, one at a time, into the chocolate mixture until combined.
Add the vanilla and stir until combined.
Sprinkle the coconut and flour mixture over the chocolate mixture. Fold the coconut and flour mixture into the chocolate with a rubber spatula.
Evenly spread the batter in the prepared baking dish. Bake on the center rack for 32-36 minutes, rotating the dish halfway through the baking time. The brownies are done when a wooden pick inserted in the center comes out clean.
Allow the brownies to cool completely before lifting them out with the parchment paper. Cut into squares and enjoy!
Recipe adapted from Brown Eyed Baker