2 lb. cooked potatoes
2 tbsp. red wine vinegar
1 tbsp. Dijon mustard
1 tsp. salt
1/2 tsp. pepper
1/4 c. olive oil
3 tbsp. minced onion
1/2 c. sour cream
1/2 c. sliced radishes, cucumber or celery
1/4 c. chopped dill

Whisk vinegar, mustard, salt and pepper together in a large bowl. Whisk in oil, then onions; add potatoes; cool to room temperature and stir in remaining ingredients.