Remove rind. Next, cut bacon into 1 ½ inch long and ¼ inch thick pieces. Simmer bacon and rind for about 10 minutes in water. Drain the water, and let them dry. Preheat your oven precisely to 450 F. Turn on the heat. Take a pan and put some oil into it. Next, put bacon into the pan and sauté it over medium heat for 2 to 3 minutes until it turn light-brown in color. Remove the bacon from heat and take it out into a dish. Set it aside. Reheat the fat left in the pan until it is almost smoking.
Take the lamb, and dry it with the help of a towel. Sauté it in the hot oil and fat until it is nicely browned on every side. Add it to the bacon you placed aside before. Brown the vegetables in the same fat. Pour out the fat. Put the lamb and bacon into the casserole and add some salt and pepper. Sprinkle flour and toss everything together in order to coat the lamb. Set the casserole in the preheat oven for about 4 minutes. Take it out, toss the meat and put it back into oven. Let it cook for another 4 minutes. Take the casserole out of the oven, and turn the heat to 325 F.
Pour in some stock and wine to cover the lamb. Add garlic, herbs, tomato paste, and bacon rind to the pot. Bring everything to a full boil using the stove. Cover the casserole and set it in the lower-third portion of your preheated oven. Regulate the heat in order to ensure that the liquid simmers slowly for about 3 hours. Test the meat with the fork. If it pierces easily, it is ready.
When the lamb is in the oven, prepare the mushrooms and onions. Melt half tablespoon of butter in a skillet and bring it to bubble. Add the onions to the butter and sauté it over medium heat for about ten minutes. Make sure that the onions are browned evenly from all sides. Pour in the white wine. Season the mixture to taste. Cover the skillet and simmer the onions for approximately 45 minutes. The onions must be perfectly tender. However, they must retain their shape when the liquid is evaporated. Set it aside.
Melt the other half tablespoon of butter in another skillet and bring it to bubble. Add the mushrooms to the butter and toss them for 4 to 5 minutes until they turn brown. Set them aside.
Finally, check if the lamb is ready. If it is tender, take the content of casserole out into a sieve. Skim the fat off the sauce. Put that sauce into a pan and simmer it until it thickens. Pour it back on the lamb. Garnish the dish using parsley, and serve with rich, noodles or mashed potatoes.
