Line a 9" square pan with aluminum foil; lightly grease foil.
Cook first 3 ingredients in a heavy saucepan over medium heat, stirring constantly, 10 to 11 minutes or until smooth. Remove from heat, and stir in orange rind, vanilla, and salt until blended. Stir in nuts.
Pour fudge into prepared pan. Cover and chill at least 4 hours or until firm. Cut fudge into squares, and store in refrigerator.