In a medium bowl, stir together flour and cocoa powder; set aside. In a large bowl, combine 4 eggs, the 2 cups granulated sugar, 1/2 cup of the chocolate-hazelnut spread, and the melted butter. Beat with an electric mixer on low to medium speed until combined. Add flour mixture; stir until smooth. Spread batter in the prepared baking pan; set aside.
Wash beaters. In another large bowl, combine 4 eggs, cream cheese, the 1/3 cup granulated sugar, and the remaining chocolate-hazelnut spread. Beat on medium speed until combined. Carefully spread over batter in the prepared baking pan.
Bake for 50 to 55 minutes or until cream cheese layer is firm and set. Cool in pan on a wire rack. Cover and chill before cutting into brownies. If desired, sprinkle brownies with powdered sugar. Makes 32 brownies.