Chewy Chocolate Chip Cookies

Ingredients

• 2 1/4 cups all-purpose flour (spooned and leveled)
• 1 1/2 teaspoons cornstarch
• 1 teaspoon baking soda
• 1/2 teaspoon salt
• 3/4 cup unsalted butter (melted and cooled for 5 minutes)
• 3/4 cup light or dark brown sugar (packed)
• 1/2 cup granulated sugar
• 1 large egg (plus 1 egg yolk at room temperature)
• 2 teaspoons pure vanilla extract
• 1 1/4 cups semi-sweet chocolate chips or chunks