In a large bowl, whisk together the flour, baking soda, cornstarch, and salt. Set this mixture aside. This ensures the baking soda and salt distribute evenly throughout the dough.

In another bowl, whisk the melted butter, brown sugar, and granulated sugar together until smooth. You should see no lumps of sugar left. Add the egg and egg yolk, followed by the vanilla extract, and whisk again. The mixture will look glossy and slightly thick.

Pour the wet ingredients into the dry mixture. Using a spatula or wooden spoon, stir until a thick dough forms. It should feel soft and slightly sticky. Fold in the chocolate chips gently. If the butter causes the chips to slip off, keep mixing — they’ll hold once the dough firms up.

Cover the bowl tightly and refrigerate the dough for at least 2 hours, or overnight if possible. Chilling helps the flavors develop and prevents the cookies from spreading too much while baking.

Preheat your oven to 325°F (163°C). Line baking sheets with parchment paper or silicone mats. If your dough chilled for longer than 2 hours, let it sit at room temperature for about 15 minutes before scooping.

Scoop about 2 to 3 tablespoons of dough for each cookie. Roll each portion into a ball, then shape it slightly taller than wide — this helps create thick, bakery-style cookies. Space them about 3 inches apart on the baking sheet.

Bake the cookies for 13–14 minutes, or until the edges are lightly golden. The centers should look soft — don’t overbake them. They’ll continue to set as they cool. Let them rest on the baking sheet for 10 minutes before transferring them to a wire rack.

While still warm, press a few extra chocolate chips on top for that perfect, picture-ready look.