Preheat the oven to 170°C(325°F), Gas Mark 3.
Heat half of the butter and oil in a large frying pan. Add the shallots and fry until they are just beginning to brown, then tip in the pancetta or bacon and fry until lightly browned. Transfer to a plate with a slotted spoon.
Place the beef pieces in a zip lock bag with the seasoned flour. Shake until well coated, then remove, shaking off any excess. Add to the frying pan and fry until lightly golden on all sides. Transfer to a casserole with a lid.
Add a little of the red wine to the frying pan and scrape the bottom to remove any sediment, then pour this on top of the beef with the rest of the red wine and the stock, carrots, celery, bay leaves and thyme. Add the sautéed shallots and pancetta and season to taste. Stir to combine, then cover with a lid and place in the oven for 2 hours, until the meat is tender but still holding its shape.
Halfway through cooking, heat the remaining oil and butter in a large frying pan and cook the mushrooms until just tender and lightly browned, stirring. Add the brandy and cook for another few minutes, then stir into the casserole and return to the oven for the remaining cooking time.
When the beef bourguignon is ready, season to taste and garnish with the thyme leaves.
Place the potatoes in a large pan of salted water. Bring to the boil, then cover and simmer for 15–20 minutes, until the potatoes are tender without breaking up. Drain and return to the pan over a low heat to dry out.
Mash the potatoes or pass them through a potato ricer or vegetable mouli if you want a really smooth finish. Heat the milk in a small pan or in the microwave. Using a wooden spoon, beat in the butter until melted, then beat the warm milk into the potatoes until you have a smooth, creamy mash. Season to taste with salt and pepper and serve at once garnished with the snipped fresh chives.
Garlic mashed potatoes are great served with main courses that already have plenty of gutsy flavours going on. Place 6 peeled garlic cloves in a pan with the milk and simmer very gently for about 10 minutes, until completely softened, then blitz to a thick purée with a hand blender and beat to the mashed potatoes.
Serve straight to the table with a separate bowl of crusty French bread to hand around.