1 1/2 cups (210 g) all purpose gluten free flour, plus more for sprinkling (I used Better Batter)
3/4 teaspoon xanthan gum (omit if your blend already contains it)
3/4 teaspoon baking powder
1/4 teaspoon kosher salt
2 cups (200 g) granulated sugar
11 tablespoons (154 g) unsalted butter, melted
1 teaspoon pure vanilla extract
1/4 cup (2 fluid ounces) lukewarm water, plus more if necessary
Preheat your oven to 325°F. In a large bowl, place the flour, xanthan gum, baking powder, salt, and granulated sugar, and whisk to combine. Add 8 tablespoons (112 g) of the melted butter, vanilla, and 1/4 cup water to the bowl, and mix to combine. The dough will come together and be soft. If you’ve used a higher starch flour blend, the dough may be stiff. If it is, add more water by the half-teaspoonful and mix until the proper texture is reached.
Divide the dough into thirds and place one piece on a large sheet of unbleached parchment paper. Sprinkle the dough lightly with flour and pat it into a thick rectangle. Dust lightly with more flour and roll the dough into a rough rectangle that’s a bit more than 1/8-inch thick (no thinner), sprinkling lightly with flour as necessary to prevent sticking. Press a nonstick grid-pattern wire cooling rack firmly onto the top of the rolled out dough to create a grid pattern on the dough. Hold down the parchment paper with one hand, and slowly peel away the cooling rack with the other hand. Using a pastry brush, brush the top of the dough generously with some of the remaining melted butter.
Place the rectangle of dough, still on the parchment paper, flat on a half sheet pan. Have a large, round, metal cookie cutter (I used a plain 3 5/8-inch cutter made by Ateco, but even a metal mason jar lid will work) ready to score the dough as soon as it comes out of the oven. Place the dough in the center of the preheated oven and bake until very pale golden all over, about 12 minutes. Remove from the oven, and immediately use the cookie cutter to cut as many rounds as possible into the dough. Twist the cutter a bit to cut all the way through the dough, but leave the dough otherwise undisturbed. Return the baking tray to the oven for another 3 minutes or until the top is more evenly lightly golden brown. Remove from the oven and allow to cool completely before breaking away the scored cookie rounds from the surrounding cookie. Crumble the scraps and use as an ice cream topper or crush completely into crumbs and use in a graham cracker-style cookie crust. Repeat with the other two pieces of dough in turn.
Adapted from this recipe for homemade gluten free Kit Kats.