This tangy salad is a traditional favorite for picnics.
1. Whisk the egg and sour cream in a small saucepan. Add the flour and stir over medium heat until the mixture bubbles and thickens slightly.
2. Meanwhile, combine the vinegar, sugar, onion, celery leaves, and bay leaf in another saucepan and boil, uncovered, at a gentle bubble for 5 minutes. Strain the liquid, then whisk it into the sour cream mixture.
3. Place the shredded cabbage in a large mixing bowl. Pour on the dressing and toss to combine. Season with salt and pepper. Cover the bowl and refrigerate until thoroughly chilled.