Step 1

Line rimmed baking sheets with unbleached parchment paper and set it aside.

Step 2

In a large bowl, place the flour blend, xanthan gum, baking soda, salt and granulated sugar, and whisk to combine well. Add the brown sugar and whisk, working out any lumps in the brown sugar.

Step 3

Add the butter, shortening, beaten egg and vanilla, and mix to combine.

Step 4

The dough will be thick and somewhat dry. Add the water by the half-teaspoonful and knead the dough with clean hands until the cookie dough holds together well.

Step 5

Add the chocolate chips to the mixture, and mix until they are evenly distributed throughout the dough.

Step 6

Transfer one-half of the dough to a large sheet of plastic wrap. Shape it into a log about 2 1/2 inches in diameter, squeezing it as tightly as possible to help it hold together well. Close the plastic wrap tightly over the log. Repeat with the other half of the cookie dough.

Step 7

Place the dough logs in the refrigerator for about 30 minutes, or just until the dough begins to firm up a bit.

Step 8

While the dough is chilling, preheat your oven to 350°F.

Step 9

If you chill the dough too long and find that it's actually hard and very solid, just let it sit, covered, at room temperature until it softens all the way to the center.

Step 10

Remove one log of cookie dough from the refrigerator, unwrap it, and roll it back and forth on the counter to round out the bottom edge, which will have flattened where it rested.

Step 11

Using a large serrated bread knife, sawing back and forth, slice the dough thickly in cross-section into rounds that are nearly 3/4-inch thick. If any of the dough has split during slicing, place the disk of dough in the palm of your hand and coax it back together into a round.

Step 12

Place the rounds about 1-inch apart on the prepared baking sheet.

Step 13

Repeat with the other log of cookie dough.

Step 14

Place one baking sheet of cookies into the center of the preheated oven and bake for about 15 minutes, or until the cookies are lightly golden brown and set.

Step 15

Allow the cookies to set on the baking sheet for about 10 minutes or until firm. They will crisp as they cool.