Butter the sides of a heavy 2-quart saucepan. Add sugar, sour cream, corn syrup, and salt to the saucepan; cook over low heat, stirring constantly, until sugar is dissolved. Turn heat up to medium; cook until mixture boils. Continue cooking, stirring occasionally until it reaches about 238 F on candy thermometer, or soft ball* stage. Remove from heat.

Add butter and vanilla without stirring; cool to lukewarm or about 110 F, then beat vigorously until fudge is creamy and no longer glossy.

Stir in cherries and walnuts.

Pour the fudge mixture into a buttered 8-inch square pan or, for thicker pieces, a 9-by-5-inch loaf pan.

Cool until firm, then cut into squares.