• 2 pounds red or brown all-purpose potatoes
• 2 tablespoons white wine vinegar
• Salt and freshly ground pepper to taste
• 2 cups Gruyère or Swiss cheese, cut in 1/4-inch cubes
• 2 cups diced celery
• Green-leaf lettuce leaves
• 1/2 cup coarsely chopped walnuts, lightly toasted
  
  Dressing:
  
• 1 cup mayonnaise, 
• 1 tablespoon Dijon mustard, 
• 1 tablespoon Worcestershire sauce

Cover the potatoes with cold water, bring to the boil and boil gently for 15 to 20 minutes, Test for doneness. Drain. 
When cool enough to handle, peel and cut into 1/4-inch cubes. Place the cubes in a large bowl. Sprinkle with vinegar, salt and pepper and let cool. Add the cheese and celery to the potatoes. Toss gently.

To make the dressing, in a small bowl, stir together the mayonnaise, mustard, and Worcestershire sauce. Add the dressing to the potato mixture and stir gently but thoroughly.

Line a bowl with the lettuce leaves. Pile the potato mixture on the greens and sprinkle with the walnuts. Cover and refrigerate for up to 2 days. Serve chilled.