In a medium bowl, whisk together 2¼ cups gluten-free flour blend, 1 teaspoon baking soda, 1 teaspoon cornstarch, and ½ teaspoon salt until well combined.

In the bowl of a stand mixer fitted with the paddle attachment, cream 1 cup softened unsalted butter with ¾ cup granulated sugar and ¾ cup packed brown sugar on medium speed until light and fluffy, about 2 minutes.

Add 1 large egg, 1 large egg yolk, and 1 teaspoon vanilla extract; beat until pale and glossy, about 1 minute.

Reduce mixer speed to low and gradually add the dry ingredients, mixing until just combined—the dough will be slightly grainy.

Fold in 2 cups semisweet chocolate chips by hand, ensuring even distribution without overmixing.

Chill dough scoops (2-tablespoon mounds) on the baking sheet for 15 minutes to prevent excess spread.

Preheat oven to 350°F. Bake chilled dough for 10–12 minutes, rotating sheets halfway, until edges are golden and centers appear slightly underbaked.

Allow cookies to cool on the baking sheet for 5 minutes, then transfer to a wire rack to cool completely.