8 tablespoons (112 g) unsalted butter, at room temperature
1/3 cup (73 g) packed light brown sugar
1/8 teaspoon kosher salt
1 cup (140 g) all purpose gluten free flour (I used Better Batter)
1/4 teaspoon xanthan gum (omit if your blend already contains it)
1/4 cup (36 g) cornstarch
Preheat your oven to 325°F. Line a large rimmed baking sheet with unbleached parchment paper and set it aside.
In a large bowl, place the butter, brown sugar, salt and beat with a handheld mixer or stand mixer fitted with the paddle attachment on medium-high speed until light and fluffy (about 3 minutes). Add the flour, xanthan gum and cornstarch, and mix until just combined. The dough will seem crumbly at first, but just keep mixing until it comes together.
Press the dough into a ball and transfer it to a large sheet of unbleached parchment paper. Cover with another sheet of parchment paper and press and roll the dough into a rectangle about 1/2-inch thick. Remove the top sheet of parchment and, using a sharp knife or pastry cutter, trim the edges all around the rectangle to create a blunt edge. Slice the dough into about 16 smaller rectangles, each about 1-inch wide by 2-inches long. Using a toothpick, pierce 6 small, evenly spaced holes in each small rectangle. Transfer the shortbread pieces to the prepared baking sheet, placing them about 1-inch apart from one another. Place the baking sheet in the freezer for about 5 minutes or the refrigerator for about 15 minutes or until firm. This will help the cookies maintain their blunt edges during baking.
Place the baking sheet in the center of the preheated oven and bake for 15 minutes or until the cookies are very slightly brown on the edges and set (not glistening) in the center. Remove from the oven and allow to cool completely on the baking sheet. Dip in or drizzle the cooled cookies with melted chocolate and allow to set before serving. Store the cookies in a sealed glass container at room temperature for at least 3 days, or freeze for longer storage. If freezing the cookies, freeze them plain, without a chocolate glaze. Dip them in melted chocolate soon before serving, to prevent the chocolate from any ugly blooming (that’s where the chocolate develops a white layer, which is harmless but doesn’t look pretty).