Lamb - Ground
Heat the oil over a moderate-low heat and gently sauté the onion until transparent.
Increase the heat, add the ground lamb and sauté, breaking it up as it cooks, until well-browned. While the lamb is browning, gradually add the other vegetables in order, and the bacon. Add the bouquet garni and stock, bring to a simmer, and cook slowly, on the cooktop for about an hour. Divide the cooked meat mixture between five oven-proof serving bowls.
Enrich the mashed sweet potato with half the butter and about two-thirds of the cheese. (You may also wish to add a little milk). Spread a thick layer of sweet potato over the top of each bowl, sprinkle with the remaining cheese and dot with remaining butter. Place in a hot oven for 10-15 minutes, until the top is crusty and golden. Serve with vegetables of your choice.