Place the lamb in a mixing bowl.
02Heat two tablespoons of the oil in a small skillet and add the onions and garlic. Cook briefly, stirring, until wilted. Sprinkle with cumin and stir, blending well. Cool briefly.03Scrape the onion mixture into the lamb. Add the coriander, bread crumbs, egg, salt and pepper. Blend well with fingers and shape the mixture into 20 patties. Set aside.04For the mushroom sauce, heat the butter in a saucepan and add the mushrooms, shallots, salt and pepper. Cook over medium-high heat until all the moisture from the mushrooms has evaporated.05Add the wine and simmer briefly over high heat. Add the tomatoes, broth and tarragon. Cook about 5 minutes, stirring occasionally.06Blend the arrowroot with the water. Stir into the sauce and cook briefly.07Meanwhile, heat the remaining olive oil in a nonstick skillet large enough to hold the patties in one layer. Add the patties and turn them so they brown evenly, about 5 minutes. Drain the fat.08Add the patties to the sauce, cover and simmer about 10 minutes.