Boil the potatoes until done. Peel them if the skins are old and tough. Cool and dice.
Dice the smoked salmon. Separate the egg white from the egg yolk. Chop the egg white; set the egg yolk aside until later.
In a large bowl, combine the diced potatoes, diced salmon, and chopped egg white. Sprinkle with freshly ground pepper. In a small dish, dissolve the salt in the lemon or lime juice; add the mayonnaise and mix well. Stir the mayonnaise mixture into the ingredients in the large bowl.
Place the salad on beds of lettuce and watercress. Put the egg yolk in a sieve and sprinkle on the salad by pushing it through with a pestle or spoon. Serve with crusty bread.
Beverly Pepper, The Glamour Magazine After Five Cookbook, 1952
The somewhat excruciating method is to ensure that the flavorings are evenly distributed throughout the salad; potato-based salads have a tendency to clump.http://macheads2.net/recipes/SmokedSalmonSalad.html