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

In a large bowl, place the flour, xanthan gum, cornstarch, baking powder, and salt, and whisk to combine. Set the dry ingredients aside.

Place the cream and egg in a separate container (a measuring cup works great) and whisk to combine well.

Create a well in the center of the dry ingredients, pour in the cream and egg mixture, and mix until just combined.

The biscuit dough will be very thick and rather lumpy, and may become difficult to stir. Mix until just combined.

Scoop the dough into large mounds, about 3 heaping tablespoons each, and place on the prepared baking sheet about 1 1/2-inches apart from one another.

Brush the tops and sides of the mounds with a bit more cream to help the biscuits brown in the oven.

Place in the center of the preheated oven and bake for about 15 minutes, or until the outsides are beginning to brown and the tops spring back when pressed lightly in the center.

Remove from the oven and allow to cool briefly before serving warm.