In a large bowl, whisk together flour, soda, cornstarch, and salt.

In another medium bowl, use a whisk or electric beater to beat together butter and sugars until no lumps remain. Add egg, yolk, and vanilla extract and continue to beat until smooth. Slowly stir in flour until batter comes together. Stir in your choice of chocolate chips and chunks.

Chill dough for at least 2 hours or overnight. If you're in a hurry, scoop 2 Tablespoons of dough in round balls onto cookie sheets and freeze for 15 minutes before baking.

When ready to bake, preheat oven to 325 degrees. Line 2 large cookie sheets with parchment paper. Bake for 10-12 minutes, rotating the pans halfway through. The cookies will look soft and underdone. That's okay. Allow them to set up on the baking sheet for 3-4 minutes then remove to a wire rack to cool completely.