3/4 cup commercial eggnog
2 tablespoons white corn syrup
2 tablespoons butter
2 cups granulated sugar
1 teaspoon vanilla extract

Butter an 8-inch square pan. Lightly butter sides of heavy, medium saucepan.

Combine eggnog, corn syrup, butter and sugar in prepared saucepan. Cook over medium heat, stirring constantly, until sugar is dissolves and mixture comes to a boil. Wash down sides of pan with pastry brush frequently dipped in hot water to remove sugar crystals.

Clip a candy thermometer to the saucepan. Continue to cook until mixture reaches the soft-ball stage (238 degrees F). 

Pour into large heatproof mixer bowl. Cool to lukewarm, (about 110 degrees F). Add vanilla extract and beat with heavy-duty mixer until thick. Spread into prepared pan. Score fudge into squares with knife. Refrigerate until firm. Cut into squares. Store in refrigerator.

Yields about 1 pound.