1 Lightly butter bottom and sides of an 8-inch square pan. Set aside. 2 Place marshmallows and butter in mixing bowl. Heat on High power 1-2 minutes until marshmallows are puffy and softened. 3 Stir cereal, walnuts and cranberries into marshmallows. 4 Mix well. Pour into prepared pan. Rub a little butter onto fingers and press mixture evenly into pan. 5 Make the chocolate frosting by placing chocolate chips in a microwave-safe bowl. Heat on High power 1-2 minutes until chips are softened, not melted6 Stir until chips are smooth and melted. Spread on top of Walnut Berry Bars.7 Press walnut halves on chocolate, placing in even 4x4 rows. Cool. Cut into 16 squares so there is one walnut half on each square.