4 green onions, finely chopped
In a large bowl, stir the vinegar, sugar, salt, and pepper until the sugar dissolves. Add the cabbage and carrots and toss to thoroughly coat with the dressing. Cover with plastic wrap and refrigerate for 30 minutes.
In a small bowl, stir the crème fraîche, mayonnaise, and mustard to blend. Drizzle the mayonnaise dressing over the cabbage mixture and toss to combine thoroughly. Mix in the green onions and serve.