1 lb. of cold boiled potatoes, 6 hard-boiled EGGS, the juice of 1/2 a lemon, pepper and salt to taste. Cut the potatoes and EGGS into slices, dust them with pepper and salt, add the lemon juice, and mix all well together. Make the mayonnaise as follows; 1-1/2 gills of good SALAD oil, the yolks of 2 EGGS, 1 saltspoonful of mustard, lemon juice, pepper, and salt to taste. Take a clean cold basin, and place in it the yolks of the EGGS beaten up. Drop the oil into them, drop by drop, stirring with a wooden spoon quickly all the time. Great care should be taken, especially in the beginning, as the EGGS easily curdle when the oil is stirred in too fast. When the mayonnaise gets very thick add carefully a little lemon juice to thin it down, then add again oil and lemon juice alternately until all the oil is used up. Smooth the mustard witha little lemon juice, and stir it in last of all with sufficient pepper and salt. Taste the mayonnaise, and add lemon juice or seasoning as required. Vinegar may be used instead of lemon juice if the latter is not conveniently had. The mayonnaise should be made in a cold room, as it may curdle if made in a hot room. Should an accident happen, beat up another yolk of egg and start afresh with a little fresh oil, and when going on well stir in, drop by drop, the curdled mayonnaise. Mix part of it with the EGGS and potatoes, and pour the rest over the SALAD; garnish with watercress.
The Allinson Vegetarian Cookery Book, by Thomas R. Allinson (Year 1915)