I believe this one is from James Beard. I think mayonnaise replaced these salad dressings when it became commercially available.
BOILED SALAD DRESSING
2 Tbsp sifted flour
3 Tbsp sugar
1 tsp. dry
mustard
1 C. white wine
1/3 C. lemon juice or vinegar
2 eggs, separated
1/3 C. olive oil
salt & pepper
1/2 C. sour cream
Combine the flour, sugar, mustard, white wine and vinegar or lemon juice together in the top of a double boiler. Add the egg yolks, oil salt and pepper to taste. Heat over hot water until the mixture thickens. Beat the egg whites until stiff. add the sour cream and the stiffly beaten egg whites to the mixture and beat with a whisk or wooded spoon until the dressing is thoroughly blended. This can be served hot or cold.