Easy Homemade Brookie Cookies

Ingredients

• ½ cup (113g) unsalted butter, room temperature
• ¾ cup (150g) light brown sugar, packed
• ¼ cup (50g) granulated sugar
• 1 large egg, room temperature
• 1 teaspoon vanilla
• ⅓ cup Dutch-process cocoa powder
• 1 cup (125g) all-purpose flour, spooned and leveled
• ¾ teaspoon baking soda
• ½ teaspoon salt
• ⅔ cup semi-sweet chocolate chips
• 2¾ cups (345g) all-purpose flour
• 1 teaspoon cornstarch
• 1 teaspoon baking soda
• 1 teaspoon salt
• 1 cup (226g) unsalted butter, cold and cubed
• ⅔ cup (130g) granulated sugar
• 1 egg plus 1 egg yolk, room temperature
• 2 teaspoons vanilla
• 1 cup semi-sweet chocolate chips
• Flaky sea salt for sprinkling (optional)