In a large bowl, toss together the flour, baking soda, cornstarch and salt. Set aside.

In a medium sized bowl, whisk together the melted butter, brown sugar, and granulated sugar. When sugar clumps disappear, whisk in the egg, egg yolk, and vanilla.

Pour the wet ingredients into the dry ingredients and mix together with a large spatula. Fold in the chocolate chips and stir until evenly dispersed.

Chill the dough: roll the chilled dough into balls4 (I use this #50 cookie scoop for all of my standard size cookies) and place balls of dough onto a large baking sheet, large platter, or something else flat that you can stick in the refrigerator so the dough can chill. You could also chill the whole bowl of dough, but this dough is difficult to scoop once chilled, and chilling is mandatory. Cover the dough balls/bowl of dough and chill in the refrigerator for at least 2 hours and up to 3 days.

When you are ready to bake the cookies, move a rack to the middle position in the oven, then preheat it to 350ºF (177ºC). Line two large baking sheets with parchment paper or silicone baking mats and set aside.

Place no more than 8 balls (with a preference of 6) of dough onto each cookie sheet. If you like, you can press a few more chocolate chips on top/sides of the dough balls for aesthetic purposes. Keep dough/dough balls that are waiting to bake chilled.

Bake the cookies for 10-11 minutes or until edges just start to turn brown. Remove from oven and allow cookies to cool on the baking sheet for 5-10 minutes before moving to a wire rack to cool completely. You can reshape cookies while they are hot using a round cookie cutter or the rim of a mug or glass if they're more misshapen than you prefer. Store cookies in an airtight container at room temperature, up to 7 days. Baked cookies may be frozen up to 3 months. You may also freeze rolled cookie dough up to 3 months. Bake frozen for 11-12 minutes.