Heat the oil in a large pan, brown the meat well. Remove to a pot. Next sauté half an onion, leeks, carrots and celery. Add to the meat plus the garlic. Pour in the stock and stout, season. Simmer gently for approx. 1 ½ hours. Remove the meat from the pot. Strain the liquid. Discard the vegetables.
Place the meat back in a clean pot, plus the liquid. Sauté the bacon, mushrooms and remaining onion in 25g butter. Add to the pot. Reheat the lot. Blend the flour with remaining butter. Stir it into the sauce, stirring well. Taste for seasoning. Serve in a deep dish with buttery mash.