3/4 c. olive oil or vegetable oil
1/4 c. tarragon vinegar
1 tbsp. chopped watercress leaves
1 tbsp. chopped parsley
1 tbsp. Dijon-style mustard
1 tsp. prepared horseradish
2 tbsp. capers, drained
1/2 tsp. salt
1/4 tsp. coarsely ground pepper
1 lb. onion, thinly sliced

In a small bowl, combine oil, vinegar, watercress, parsley, mustard, horseradish, capers, salt and pepper. Place beef in a firm plastic container with a tight-fitting lid. Top with onion. Pour marinade over beef and onion. Cover with foil or plastic wrap. Complete now or make ahead.

To complete now, refrigerate 3 to 4 hours. Drain off and discard about 1/2 of marinade; arrange meat and onion on a platter or serving plate with a rim or sloping sides to keep marinade contained. Pour reserved marinade over meat and onion. Serve cold.

To make ahead, refrigerate up to 24 hours; serve as directed above. Makes about 6 servings.