In a large bowl, stir 1/4 cup of boiling water into the gelatin, stirring until completely dissolved. Add the ice cube and stir constantly for 3 to 5 minutes or until mixture is slightly thickened. With a slotted spoon, remove any unmelted ice. Stir in the sour cream until well blended. Set aside the following: 1/2 cup pineapple, 1/4 cup of mandarin orange sections, and 1 Tbls of chopped walnuts, for the garnish. Stir in the remaining ingredients and pour into an 8-inch square baking dish topping with the garnish mixture that you set aside. Refrigerate at least 4 hours or overnight until firm.
