Season the cutlets with salt and pepper, brush them over with melted butter or fat with the aid of a pastry brush, and then dip them in stale crumbled bread, patting it on to have a thick coating.
Grill for 4 or 5 minutes each side.
Boil the white part of the leeks in salted water, then chop very finely, and dry thoroughly on a cloth.
"Melt" them in a deep frying pan or saucepan with 3 tablespoons of fat so they become soft and transparent, not brown.
Stir in the flour, season, heat, and then, away from the heat, stir in the egg yolks.
Pour into your serving dish.
Serve the cutlets on this creamy mixture (which you keep hot till the cutlets are ready by standing the dish in another vessel filled with hot water).