In a large bowl, place the flour, xanthan gum, cornstarch, baking soda and salt, and whisk to combine well. Transfer 1 tablespoon of the dry ingredients to a small bowl, and toss with the chocolate chips, then set the chips aside.

To the large bowl of dry ingredients, add the granulated sugar and brown sugar, and whisk to combine well, breaking up any lumps in the brown sugar.

Create a well in the center and add the butter, vanilla and eggs, mixing to combine after each addition. The dough should be thick but soft. If your dough isn’t coming together properly, your butter and eggs most likely were too cold.

Allow the dough to sit until the ingredients warm up, and then bring it together.

Add the chocolate chips and reserved dry ingredients, and mix until the chips are evenly distributed throughout the dough.

Cover the dough and place it in the refrigerator to chill until it is easier to handle (about 10 minutes).

In a large bowl, place the flour, xanthan gum, cocoa powder, baking soda and salt, and whisk to combine well.

Transfer 1 tablespoon of the dry ingredients to a small bowl, and toss with the chocolate chips, then set the chips aside.

To the large bowl of dry ingredients, add the granulated sugar and brown sugar, and whisk to combine well, breaking up any lumps in the brown sugar.

Create a well in the center and add the butter, oil, vanilla and eggs, mixing to combine after each addition. The dough should be thick but soft.

Add the chocolate chips and reserved dry ingredients, and mix until the chips are evenly distributed throughout the dough.

Cover the dough and place it in the refrigerator to chill briefly until it is easier to handle (about 10 minutes).

Once the dough has chilled, divide both types of dough into mounds that are about 1 teaspoonful each (I used a #70 ice cream scoop to do this, and it was the perfect size).

You should get about 36 mounds of each type of dough. If the dough becomes too sticky to handle, try placing the mounds in the freezer briefly.

Pair 1 mound each of chocolate chip cookie dough with 1 mound of brownie dough, side by side.

Roll together into a ball between your palms, press gently into a disk about 1/2-inch thick, and place on a prepared baking sheet.

Repeat with the remaining mounds of dough, placing them about 1 1/2-inches apart on the prepared baking sheets.

Place the baking sheets, one at a time, in the center of the preheated oven and bake for about 12 minutes, or until set in the center and just beginning to brown on the underside of the chocolate chip cookie side (you won’t be able to detect the browning on the brownie side).

Remove from the oven and allow to cool for 5 minutes on the baking sheet before transferring to a wire rack to cool completely.