Brownie Batter Filling

• ½ cup heat-treated all-purpose flour
• ¼ cup unsweetened cocoa powder
• ⅓ cup powdered sugar
• 2 tablespoons light brown sugar
• ¼ teaspoon salt
• ¼ cup butter, melted and slightly cooled
• 1 tablespoon milk
• ½ teaspoon vanilla extract
• ¼ cup mini chocolate chips

Chocolate Cookie Dough

• 3 cups all-purpose flour
• ½ cup unsweetened cocoa powder
• 1 tablespoon cornstarch
• 1 teaspoon baking soda
• ½ teaspoon baking powder
• ¾ teaspoon salt
• 1 cup cold butter, cubed
• 1 cup light brown sugar
• ½ cup granulated sugar
• 2 large eggs
• 1 tablespoon vanilla extract
• 1 cup milk chocolate chips
• 1 cup dark or semi-sweet chocolate chips