For the beef bourguignon, sprinkle the flour onto a plate and season with salt and freshly ground black pepper. Dredge the beef in the seasoned flour and set aside. Heat one tablespoon of the oil in a large, lidded frying pan and fry the pancetta for 1-2 minutes, or until golden-brown. Add the beef and fry for a further 4-5 minutes, or until browned on each side. Add the shallots and garlic and fry for 4-5 minutes, or until just softened. Add the brandy and slowly tilt the pan towards the gas flame, or light it with a match. Let the flames flare up then die down. (Caution: keep your face and hair away from the flames. Do not leave unattended.) Add the red wine and beef stock and bring to a simmer. Add the bouquet garni, then cover and cook on a low heat for two hours, or until the beef is tender and the sauce has thickened. Heat the butter and remaining oil in a frying pan and fry the baby onions for 4-5, or until just golden-brown. Add the browned onions and the chestnut mushrooms to the beef mixture and cook for a further 20 minutes. Season, to taste, with salt and freshly ground black pepper. Meanwhile, for the mash, cook the potatoes in a pan of boiling salted water for 12-15 minutes, or until the potatoes are tender. Drain and return to the pan, then place over the heat for one minute to drive off any excess moisture. Mash the potatoes well, then add the butter and milk and beat with a wooden spoon until smooth. Season, to taste, with salt and freshly ground black pepper. For the garnish, heat the olive oil and butter in a small frying pan. Add the onions and fry until brown. Add the pancetta and fry until browned and crisp. Then add the mushrooms and continue frying until the mushrooms are softened and golden-brown. Finish with the chopped parsley and set aside until ready to serve. To serve, divide the mash equally among the serving plates and spoon the beef bourguignon alongside, with the garnish on top.