Fry the pancetta and onions. Cook until tender and the pancetta has begun to crisp. Add the garlic and chillies. Cook for a minute, then transfer to a casserole dish.
Brown the beef on all sides, then add the flour and stir in. Add to the casserole dish.
To the casserole, add the stock, tomatoes, chilli powder, sugar and cinnamon. Cover with a tight lid, then braise on the middle shelf of the oven for 1½ hours.
Remove from the oven and stir through the chocolate until melted.