PREPARATION:
- Butter 8-inch square pan; set aside. Lightly butter side of heavy medium saucepan.
- Combine sour cream, milk, corn syrup, butter and sugar in prepared saucepan. Cook over medium heat, stirring constantly, until sugar dissolves and mixture comes to a boil. Wash down side of pan with pastry brush frequently dipped in hot water to remove sugar crystals.
- Add candy thermometer. Continue to cook until mixture reaches soft-ball stage (238°F).
- Pour into large heatproof mixer bowl. Cool to lukewarm (about 110°F).
- Add vanilla and beat with heavy-duty electric mixer until thick. Spread into prepared pan. Score fudge into small squares. Refrigerate until firm.
- Cut into squares. Place walnut half on each piece. Refrigerate.
