Make the dressing: Whisk the vinegar, mustard, sugar, 1 teaspoon salt and 1/2 teaspoon pepper in a large bowl. Gradually whisk in the olive oil until well blended.
Add the cabbage, parsley, scallions and grapes to the bowl and toss to coat with the dressing. Cover and refrigerate 1 to 4 hours before serving.
Photograph by Yunhee Kim
Recipe courtesy Food Network Magazine