Add about 2 tablespoons of olive oil and a good sized knob of butter to a hot, thick bottomed saucepan large enough to fit your joint with ample space around it. Brown the pork on all sides and get a nice caramel colour to it. Remove from the pan and reserve.
Soften the onions or shallots in the same pan. Add thyme, juniper berries, cloves, apple, chicken stock, dry cider and the pork; season to taste. Simmer, covered, for about 30 minutes.
Add the prepared celariac and cook, covered, for another 40 minutes. If you need more fluid at this stage add another glug of cider.
Make a beurre manie by mashing plain flour together with some butter at room temperature. Mix until it is a moist pale yellow paste.
Remove the pork and keep warm. Remove the berries, cloves and thyme and whisk in the beurre manié bit by bit until it has all been incorporated into the simmering liquid. Check seasoning. Stir continuously for about 2 minutes then add the cream and bring to the boil.
Slice the pork and arrange on an oval plate and spoon over the sauce. Garnish with fresh thyme and serve with roast or mashed potato and green veg.
You can also make this without the berries and cloves. Try experimenting with different flavours like chilli and paprika or just on its own with parsley.