FISH A LA CREME

From 1922:

Take a bream or any white fish, 1 teaspoon parley, 1 small onion, 1 tablespoon butter, ½ oz bacon fat, 1 gill gravy and ½ cup breadcrumbs. Slice the onion and fry in a little of the butter. Clean the fish and take out the bones, cut it in fillets, put a layer in a piedish, sprinkle with salt and pepper, put on some pieces of bacon fat, half the breadcrumbs and half the onion, then another layer of fish, bacon, onion, salt and pepper, and pour over it the gravy. Then cover with the remainder of the breadcrumbs, put the rest of the butter on in small pieces and bake in a moderate oven for half an hour.