The soup and sauce book

by Elizabeth Douglas

Genoese Sauce

(For Fillet of Sole)

1 oz. butter
2 table-spoons olive oil
2 yolks of eggs
1 table-spoon vinegar

Put the oil and butter into a sauce-pan on the fire and stir till the butter is melted. Beat the yolks slightly. Add the vinegar to them. Season. Directly the butter is melted add the yolks and vinegar, stirring continually over a bain marie until the sauce thickens. Half a tea-spoonful of mustard may be added.