Preheat oven to 325°. Grease an 8 or 9-inch square baking pan. In a medium bowl, beat together butter, sugar, eggs and vanilla until light and fluffy. Beat in melted chocolate. Add flour, beating until well blended. Stir in walnuts . Spread evenly in greased baking pan Bake 25-30 minutes. Do not overbake. Cool in minutes and then frost.
Frosting: Place 1 cup chocolate chips in blender. In a small saucepan, heat 1/2 cup of whipping cream until hot. Quickly pour cream into blender. Add 1 tsp vanilla extract; blend until chocolate melts and mixture is smooth and glossy. Refrigerate until set before cutting into squares.