Combine the vinegar, mustard, sugar, salt, pepper, sour cream, and mayonnaise in a small bowl and whisk until smooth.
Combine the cabbage, herbs, green onions, grapes, and walnuts in a large bowl and toss with the dressing. Allow to stand in the refrigerate for a couple of hours or up to overnight for flavors to meld.
Recipe by Cooking With MicheleĀ® at https://cookingwithmichele.com/2016/08/green-summer-slaw/