Combine dry ingredients. In a large bowl, whisk the flour, baking soda, cornstarch, and salt together. Set aside. 2 ¼ cups (280 g) all-purpose flour 1 teaspoon baking soda 2 teaspoons cornstarch ½ teaspoon salt
Combine butter and sugars. In a medium bowl, whisk the melted butter, brown sugar, and granulated sugar together until evenly combined. ¾ cup (1 ½ sticks, 170 g) unsalted butter ¾ cup (150 g) packed light brown sugar ½ cup (100 g) granulated sugar
Add eggs and vanilla. Whisk in the egg and egg yolk until evenly mixed in. Whisk in the vanilla extract until evenly incorporated. 1 large egg + 1 egg yolk 2 teaspoons pure vanilla extract
Add flour mixture and chocolate chips. With a spatula or wooden spoon, stir in the dry ingredients and chocolate chips and mix together. The dough will be soft and thick. 1 ¼ cup (213 g) semi sweet chocolate chips
Chill the dough. Cover the dough tightly and chill in the refrigerator for at least 2 hours up to overnight. When ready to bake, take the dough out of the refrigerator and allow it to slightly soften at room temperature for 10 minutes.
Prep oven and pans. Preheat oven to 350°F (180°C). Line large baking sheets with parchment paper or silicone baking mats. Set aside.
Scoop cookies. Using a small cookie scoop or use a measuring spoon and scoop dough into 2 tablespoons portions (about 40 g).
Bake cookies. Bake the cookies for 10-12 minutes until the edges are very lightly browned. The centers will look very soft but the edges set and golden brown. The cookies will continue to set as they cool. Cool on the baking sheet for 10 minutes. Then transfer cookies to a wire rack to cool completely..