Preheat your oven to 350°F (175°C). This step is crucial as it ensures that your cookie bakes evenly.
Line your baking sheet with parchment paper. This will help prevent the cookie from sticking and make for easy cleanup.
In a medium mixing bowl, combine the chilled unsalted butter and packed brown sugar. Use a whisk or fork to cream them together until the mixture is smooth and slightly fluffy.
Add the beaten egg and pure vanilla extract (if using) to the bowl. Mix until well combined.
In a separate bowl, whisk together the gluten-free all-purpose flour, baking powder, and sea salt. Gradually add this dry mixture to the wet ingredients, stirring until just combined. Be careful not to overmix!
Gently fold in the semi-sweet chocolate chips, distributing them evenly throughout the dough.
Using a cookie scoop or spoon, portion out the dough onto the prepared baking sheet. Shape it into a large, round mound. Remember, this is one huge cookie, so make it big!
Place the baking sheet in the preheated oven and bake for 12-15 minutes, or until the edges are lightly golden. The center may look slightly underbaked, but it will continue to cook as it cools.
Once baked, remove the cookie from the oven and let it cool on the baking sheet for about 5 minutes before transferring it to a wire rack. Enjoy warm with a glass of milk or your favorite beverage!