Remove any unnecessary fat from the loin of mutton, and take out the bones; lay it on the table and beat it out with a wet meat chopper or cutlet bat; season inside with black pepper, salt, and a little finely chopped onion or eschalot, and a little chopped lean ham or uncooked bacon. Place a layer of herb farce on the seasoning and roll it up, fasten up tightly by means of a needle and string, then put it in the oven in a buttered or greased paper in a baking tin with a little fat for about half an hour; take up and remove the paper; brush over with the whole egg beaten up, and roll it in browned breadcrumbs; put it again in the oven for about three quarters of an hour, keeping it occasionally basted; when cooked draw out the string, put the meat on the dish and serve with brown caper sauce as below, some of which serve on the dish, and some in a sauceboat. Piquant or Bourguignotte sauce may be served if preferred.
Gaper Sauce (Brown)
Put the bones with some fat that was removed from the joint to fry with onion (sliced), a little thyme, parsley, bayleaf, and three or four peppercorns, and a pinch of salt, till well browned, but not burnt: if you have any cooked meat bones put them in the pan, cover with cold water, and then let all come steadily to the boil; keep well skimmed, and boil on slowly for about one and a half hours, then remove the fat; this fat, if boiled with a little water, and any sediment taken away and put to cool, will do for frying purposes. Fry one and a half ounces of butter or fat with one and a half ounces of flour till a good brown colour, and mix in three quarters of a pint of the prepared stock, stir till it boils, then add one and a half tablespoonfuls of common brown vinegar; strain through a strainer, add two tablespoonfuls of capers and use.