• Preheat your oven to 375°F. Line a large rimmed baking sheet with unbleached parchment paper and set it aside.

Melt the chocolate.

• In a small microwave safe bowl, place the chopped chocolate and cream. Microwave the mixture on high for 30 seconds. Stir.
• If the chocolate isn’t all melted, microwave for another 15 seconds and stir again. Repeat in 15 second intervals until the chocolate is melted and the mixture is smooth and shiny. Set aside to cool slightly.

Make the vanilla cookie dough.

• In a large bowl, place 2 cups (280 g) of the flour, xanthan gum, baking powder, baking soda, salt and sugar, and whisk to combine well.
• Add the butter, egg and vanilla, mixing well after each addition. Knead the dough until it comes together.
• Divide the cookie dough into two portions, one a couple ounces (about the size of a small egg) less than the other. Set aside the larger portion of dough.

Make the chocolate cookie dough.

• Return the smaller portion of cookie dough to the mixing bowl, and add the melted chocolate mixture. Mix to combine.
• Add the remaining 2 tablespoons flour, and knead it in until it has been absorbed by the dough.

Shape the cookie dough.

• Place the chocolate dough on a lightly floured piece of parchment paper on a flat surface, and roll into a rectangle about 1/4 inch thick.
• Repeat the same procedure, separately, with the vanilla cookie dough.
• Place both pieces of rolled out dough on a large baking sheet, still on the parchment paper.
• Place both pieces of dough in the freezer for about 10 minutes, or until firm (but not rock solid, or it will begin to crack).
• Once the dough has chilled, place one piece of chilled dough, parchment side-down, on a flat surface.
• Place the other piece of dough squarely on top of the first, parchment side-up.
• Remove the top sheet of parchment. Starting at a short end of the rectangle and using the bottom sheet of parchment paper to handle the dough, roll the dough away from you and into a cylinder that is as tight as you can manage.
• Remove the parchment paper, and wrap the roll tightly in plastic wrap or parchment.
• Chill the roll of dough in the freezer for about 10 minutes, or until firm.

Slice the cookie dough.

• Remove from the freezer, and slice into 1/4-inch pieces, by cross-section. Place less than 1 inch apart on the prepared baking sheet.

Bake the cookies.

• Place in the center of the preheated oven and bake for about 10 minutes, or until the cookies are just set in the center. They will not have browned visibly.
• Allow to cool until firm on the baking sheet before transferring to a wire rack to cool completely.