Line 13x9-inch baking pan with foil, with ends of foil extending over sides of pan to form handles. Grease foil.
Microwave unsweetened chocolate and butter in large microwavable bowl on HIGH 2 minutes or until butter is melted. Stir until chocolate is completely melted. Add sugar; mix well. Stir in eggs and vanilla. Add flour and nuts; mix well. Spread into prepared pan.
Bake at 350 degrees F for 30 to 35 minutes or until toothpick inserted in center comes out with fudgy crumbs. (Do not overbake.) Immediately drop marshmallow creme by spoonfuls over hot brownies; spread evenly over top of brownies. Cool in pan. Lift out of pan onto cutting board using foil handles. Remove foil. Place on serving tray. Drizzle melted chocolate over marshmallow creme to create a spider web design. Cut into 32 brownies just before serving.