SARDINES À LA PIEDMONT

Skin a dozen sardines and put in the oven to heat. Put into a saucepan the yolks of four eggs well beaten with one teaspoonful each of malt vinegar, tarragon vinegar, and made mustard. Add a pinch of salt, and a tablespoonful of butter. Stir until thick, but do not boil. Put the sardines on circles of fried or toasted bread, pour the sauce over, and serve.