
In a large saucepan, bring sugar and water to a boil over medium heat, stirring to dissolve sugar. Reduce heat; simmer, uncovered, 3 minutes. Carefully stir in all remaining ingredients except walnuts; return to a boil. Reduce heat; simmer, uncovered, until mixture reaches desired thickness, 20-25 minutes, stirring occasionally.
Serve warm or cold. Stir in walnuts before serving.