Butter the sides of a heavy, 2-quart saucepan; add sugar, sour cream, corn syrup, and salt. Cook, stirring constantly, over low heat until sugar is dissolved, about 5 minutes. Increase heat to medium and cook until mixture comes to a boil. Cook, stirring occasionally, until mixture reaches 239 degrees F (115 degrees C) or until a small amount of sugar mixture dropped into cold water forms a soft ball that flattens when removed from the water and placed on a flat surface. Remove saucepan from heat.
Stir butter and vanilla extract into sugar mixture and cool to lukewarm, about 110 degrees F (43 degrees C). Beat mixture vigorously until fudge is creamy and no longer glossy. Fold cherries and walnuts into fudge; pour into the prepared 8-inch pan. Allow to cool until hardened, at least 1 hour.
After cooking and cooling, the fudge is a very light caramel color and texture, but once it is properly beaten, it will become lighter in color and have the stiff texture of fudge. If you don't achieve the correct results when beating by hand, try using an electric mixer next time to make the job easier.
Per Serving: 248 calories;9.2 g fat;
41.9 g carbohydrates;
1.4 g protein;
14 mg cholesterol;
127 mg sodium.