Up to three days before you plan to make the Tagine, massage the lamb shoulder with the salt and let it sit in the refrigerator before you cook it.
To make the Tagine, in a heavy-duty Dutch oven, heat a few tablespoons of oil and sear the lamb pieces very well, turning them only after they’re nicely dark, browned, and crusty (this helps add flavor to the Tagine.) As you cook them, don’t crowd ’em in. If your Dutch oven isn’t big enough to cook them all in a single layer at once, brown the lamb pieces in batches.
Preheat the oven to 350 degrees (175 C). Once the lamb is browned, add the onions and some of the stock, then scrape the bottom of the pan with a flat wooden spatula to release the flavorful browned bits. Add the remaining stock, then the spices, the bunch of cilantro, and the saffron.
Cover the pan and bake in the oven for 2 1/2 to 3 hours, turning the lamb over in the liquid a few times during the oven-braising. The liquid should just be steaming-hot and simmering gently. If it’s boiling, turn down the heat (some Dutch ovens conduct heat differently.) When the meat starts to fall apart easily, that’s when it’s ready. It’s hard to overcook lamb shoulder, so even an extra hour or so in the oven won’t hurt it.
Remove the lid and let the Tagine remain in the oven for another 30 minutes, so the juices reduce, becoming rich and savory.