But the meltaway cookies are so incredibly easy, and so perfectly delicate that I think you should seriously consider making a double batch of this dough. Make half into these delightful little meltaways (they really do melt in your mouth), and …
Preheat your oven to 350°F. Line a large rimmed baking sheet with unbleached parchment paper and set it aside.
Make the dough. In a large bowl, place the flour, xanthan gum, cornstarch, baking powder, salt and confectioners’ sugar, and whisk to combine well. Create a well in the center of the dry ingredients and add the butter, egg white and vanilla, mixing to combine after each addition. The dough will be thick and smooth. Add water by the half-teaspoonful and knead it in with clean, dry hands as necessary to bring the dough together. Add the (optional) chocolate chips and knead into the dough until they are evenly spaced throughout.
Shape the dough. Scoop the dough by the heaping tablespoon (an overfull #70 ice cream scoop is ideal here, but two spoons work well, too) onto the prepared baking sheet, leaving about 1 1/2-inches between pieces. Roll each piece of dough into a round between the palms of your hands, and press down slightly into a thick disk. With the moistened tines of a fork, press down on the top of each piece of dough until the tines leave an impression about 1/4-inch deep.
Bake. Place the baking sheet in the center of the preheated oven and bake until lightly golden brown on the edges and firm to the touch (about 12 minutes). Remove from the oven and allow to cool completely on the baking sheet.