Drain pineapple, reserving juice; set pineapple aside. In a saucepan, combine sugar and cornstarch; stir in pineapple juice until smooth. Bring to a boil over medium heat; cook and stir for 2 minutes or until thickened and bubbly.
Remove from the heat; stir in the butter, vinegar, salt and pineapple. Serve over ice cream; sprinkle with walnuts.