2½ cups sugar
1¼ cups heavy whipping cream
1/3 cup Karo light corn syrup
½ tsp. salt
1 Tbsp. butter
1 Tbsp. vanilla extract
1 cup chopped walnuts (optional)
Butter an 8 x 8-inch square pan or line pan with buttered foil; set aside.
Combine sugar, cream, corn syrup, salt and butter in a heavy 3-quart saucepan. Cook over medium heat, stirring frequently until mixture boils. Continue cooking, stirring occasionally until candy thermometer reaches 235 to 240°F (soft ball stage). Remove from heat; do not remove candy thermometer.
Cool mixture to 100°F. (TIP: To speed cooling, place pan of hot fudge mixture in a cold water bath.) Remove candy thermometer.
Add vanilla. Beat mixture with a wooden spoon until it thickens and begins to lose its gloss (about 4 to 5 minutes). Stir in walnuts.
Pour fudge mixture into prepared pan. Cool completely. When firm, remove from pan; cut into squares.
(Makes 36 pieces)