Put the flour on a large plate and season liberally with salt and pepper. Toss the beef cubes in the flour until they are lightly coated.
Add a good splash of oil in a large casserole dish and brown the beef cubes over medium high heat. Don't crowd the beef in the pan as it will steam rather than brown. Transfer to a plate and set aside.
Add a splash of stock to the pan and scrape any sticky flour/beef bits with a wooden spoon.
Add the chopped shallots, and a splash more oil if needed, and cook for 4-5 minutes.
Add the prunes, carrots, parsnips, garlic, apple, chestnuts and bay leaves and continue to cook for another 5 minutes, adding stock if the pan is dry.
Stir in the tomato paste, vinegar and orange peel. Add the beef and pour in the stock and wine.
Bring to the boil, cover the casserole and put in the oven for 1 1/2 –2 hours.
Remove from the oven, check the seasoning and remove the bay leaves.
While the stew is cooking, make the mash. Put the celeriac, parsnip and garlic in a pot, and pour in enough water to cover the vegetables.
Cover the pot and bring to a boil. Reduce the heat and simmer for 15-20 minutes or until the vegetables are cooked through.
Drain and put the vegetables in a Vitamix or food processor together with the butter and a good glug of double cream. Blitz until smooth, adding a little more cream if the mash is too thick. Add salt and pepper to taste.
Divide the mash between your plates and top with the stew. Sprinkle with chopped parsley and serve.