Position an oven rack in the center of the oven. Preheat the oven to 350°F. Line two jellyroll pans with parchment paper or silicone baking mats.
In a stand mixer fitted with the whisk attachment, beat the egg yolks with the ½ cup granulated sugar on high speed until a slowly dissolving ribbon is formed on the surface when the beaters are lifted. Fold in the vanilla. In a clean bowl with clean beaters, beat the egg whites until stiff peaks form; add the 1 tablespoon granulated sugar and whisk for about 30 seconds more, or until the peaks are glossy.
In a small bowl, combine the sorghum flour, cornstarch, tapioca flour, baking powder, guar gum, and salt and stir with a whisk to blend. In three separate batches, sprinkle the dry ingredients over the egg whites and gently fold in with a rubber spatula. Repeat with the egg yolk mixture. Spoon the batter into a pastry bag fitted with a 1-inch plain pastry tip. Pipe 4½-inch-long fingers 1 inch apart on the prepared pans. You should have 12 fingers. Dust with confectioners’ sugar and bake one pan at a time for 20 minutes, or until the cookies are firm and lightly browned.
Remove from the oven. Transfer the cookies to a wire rack to cool completely. Repeat to cook the remaining batter.