Butter sides of a heavy 3-quart saucepan.
Add sugar, marshmallows, eggnog, butter, corn syrup, and salt to the saucepan; cook over low heat, stirring constantly, until sugar is dissolved.
Turn heat up to medium and cook until mixture boils. Continue to cook, stirring constantly, to about 232° .
Add chocolate chips and continue to cook for 5 minutes (should be at soft ball stage), or until chocolate is melted.
Stir in chopped nuts.
Pour into a buttered 8-inch square pan.
Cool to room temperature, then chill and cut into squares.
