Toss the meat in the seasoned flour and brown it in the olive oil. Put it in a heavy ovenproof casserole.
Fry the onions until brown, and pour the stock over them. Bubble until it is slightly reduced, scraping up any bits stuck to the pan. Add the wine vinegar, raisins or sultanas, nuts and chocolate. Stir until the chocolate has melted, and pour over the meat.
Cook in a low ove