Line two baking sheets with silicone baking mats or parchment paper. Set aside.

Place the butter, granulated sugar, and brown sugar in a medium bowl. Use a mixer to beat on medium speed until well combined, about 1 minute.

Add the egg and vanilla extract and continue to beat until smooth, about 30 seconds.

Add the gluten-free flour, cornstarch, baking soda, and salt to the bowl. Beat on low speed, scraping the sides of the bowl with a rubber spatula as needed, until a smooth dough forms.

Fold in the chocolate chips.

Preheat the oven to 350°F.

Divide the cookie dough into 30 balls, using roughly 1 1/2 tablespoons of dough for each, and arrange them spaced 1 1/2 inches apart on the baking sheets. Transfer the sheets to the freezer for 10-15 minutes. Alternately, freeze dough balls on a small tray or large plate and transfer to baking sheets after freezing.

Bake the cookies on middle rack of oven until puffy and golden brown at the edges, 15-17 minutes.

Check to see that cookies are done. Remove from oven or add time as needed.

Allow the cookies to rest on the sheets for 5-10 minutes, then transfer to a wire rack to cool completely before serving.