Ice Cream Sandy

- 1⅓ cups (187g) high-quality all-purpose gluten-free flour - ¾ teaspoon xanthan gum (omit if your blend already contains it) - ¾ teaspoon baking soda - ¼ teaspoon kosher salt - ½ cup (109g) packed light brown sugar - ¼ cup (50g) granulated sugar - 4 tablespoons (56g) unsalted butter, melted and cooled - 4 tablespoons (48g) vegetable shortening, melted and cooled - 1 extra-large egg + 1 extra-large egg yolk at room temperature, beaten - 2 teaspoons pure vanilla extract - 1 cup (6 ounces) semi-sweet chocolate chips, tossed with ½ teaspoon cornstarch