Preheat an oven to 325°F.
Heat a sauté pan medium-hot, add the olive oil, and sautè the lamb about 1 minute to brown it on all sides. Season with a little salt. Do not allow the fond (browned residue on the bottom of the pan) to get too dark. Turn the heat to low and remove the lamb to a heavy oven-proof casserole.
Add the butter to the sautè pan along with the minced onions and carrots. Sautè over low heat for a minute or two until the vegetables become light golden brown. As you stir, scrape up the fond, which should release from the pan.
Add the garlic, sautè a few seconds longer, and then stir in the flour. Cook, stirring, until the flour becomes light brown in color.
Stir in the stock slowly, to avoid forming lumps. Add the tomato purée and reduced wine. Bring the sauce to a simmer and season with a little salt. Cook about 5 minutes until the sauce lightly thickens.
Pour the sauce over the lamb in the casserole. Add the bay leaf, thyme sprigs, sage sprigs, and orange zest strips and stir to submerge them in sauce.
Cover the casserole and bake for 30 minutes.
Remove the casserole from the oven. Check the consistency of the sauce and, if getting too thick, stir in a little water.
Cover the casserole and return it to the oven. Bake about 15 minutes longer.
Remove from the oven and check the doneness of the lamb. It should be tender, so that a knife inserted meets with just a little resistance.
If necessary, adjust the consistency of the sauce: if too thick, thin out with a little water. If too thin, pour off most of the sauce into a sauté pan and reduce to a nappé [glossary link] consistency.
Taste, evaluate seasoning, and correct the salt if necessary.
If prepping ahead, cool the ragoût to room temperature and store in a container.