Butter sides of a heavy 1-quart saucepan; add sugar, sour cream, corn syrup, and salt. Cook over low heat, stirring constantly, until sugar is dissolved. Reduce heat to medium and cook until mixture boils. Continue cooking, stirring occasionally, until mixture reaches 230-240 degrees on a candy thermometer. Remove from heat.
Add butter and vanilla. Cool to lukewarm (110 degrees) without stirring. Beat vigorously until candy is creamy and loses its gloss. Stir in cherries and walnuts. Pour into buttered 8-inch square pan. Cut into squares when hardened.