SALMON MAYONNAISE

From 1922:

A tin of salmon (good brand), 2 lettuce, 1 egg, 2 or 3 spring onions, half a pint of frying or salad oil, pepper and salt, and a little vinegar.
Break the egg and separate the white from the yolk. Put the yoke into a deep basin; add frying oil, a drop at a time, rubbing hard all the time with the tip of a wooden spoon. When the oil is in, add pepper and salt to taste, a little vinegar, also liquid drained from salmon: this makes sauce a pretty pinkish color. Empty the salmon from the tin, and flake into small, neat pieces; do not mash. Have lettuces well washed, and tear up finely; add salt to taste, and finely chopped onions. Then add mayonnaise sauce, mix well in, very lightly but thoroughly, and serve at once. This dish is delightful for dinner or supper.