Gather the following ingredients:

• 2 and 1/4 cups all-purpose flour
• 1 teaspoon baking soda
• 1 and 1/2 teaspoons cornstarch
• 1/2 teaspoon salt
• 3/4 cup unsalted butter, melted and cooled
• 3/4 cup packed light or dark brown sugar
• 1/2 cup granulated sugar
• 1 large egg + 1 egg yolk, at room temperature
• 2 teaspoons pure vanilla extract
• 1 and 1/4 cups semi-sweet chocolate chips or chocolate chunks