For the salad
2 pounds halved fingerling potatoes
4 bacon slices
1 cup diced Vidalia onion
1/2 cup each red wine vinegar and beef broth
1/4 cup olive oil
1 tablespoon Dijon mustard
1/4 teaspoon dry mustard
pinch cayenne pepper
1/8 teaspoon ground celery seed
1/4 teaspoon each salt and pepper
1 cup chopped celery
1/2 cup chopped green onions
1 bunch watercress
For the sauce
1 cup yogurt
1 tablespoon prepared white horseradish
1 teaspoon red wine vinegar
1 tablespoon olive oil
1/4 teaspoon each salt and pepper
Potatoes: Par-cook and grill halved fingerling potatoes.
Dice bacon slices; cook in a skillet until just crisped. Add Vidalia onion. Caramelize onions. Remove from heat. Add red wine vinegar and beef broth, olive oil, Dijon mustard, dry mustard, cayenne pepper, ground celery seed and salt and pepper. Place cooked potatoes in a shallow baking dish. Pour bacon-onion mixture on top. Chill uncovered in refrigerator 2 hours.
Sauce: Mix yogurt with prepared white horseradish, red wine vinegar, olive oil and salt and pepper; chill until serving.
Gently stir chopped celery and green onions into potato salad. Adjust seasoning. Place in serving bowl. Top with some horseradish sauce. Sprinkle with 1 bunch watercress leaves. Serve extra horseradish sauce on the side.