This sauce is usually served with sole or other fish cooked à la normande. Make a sauce in the usual way with 2 tablespoons butter, flour and stock. Add ½ pint liquor from the cooked fish and simmer 12 to 15 minutes longer, skimming when necessary. Remove saucepan from the heat and stir in egg yolks; then whisk in 2 tablespoons diced butter. Add lemon juice, salt and freshly ground black pepper, to taste. Strain before serving.