Heat your oven to 200°C/Fan 180°C/Gas 6. Crumble the stock cube into a heatproof jug. Pour in 300 ml boiling water and stir to mix. Set aside.
Slice the roots and skin off the celeriac. Chop into small chunks. Put in a pan and cover with boiling water. Cover and bring to the boil. Simmer for 15 mins till the celeriac is soft. Drain and set aside.
While the celeriac simmers, roughly chop the apricots. Finely shred the sage leaves. Tip them both into a baking dish. Peel and thinly slice the onion and set aside.
Rub each pork chop with 1 tsp oil and season with salt and pepper. Warm a large frying pan over a high heat. When it’s smoking hot, add the pork chops. Fry for 2 mins on each side, then put in the baking dish.
Add the onion to the frying pan. Stir and fry over a high heat for 2 mins to brown them. Add to the baking dish. Pour over the chicken stock. Slide into the oven and bake for 20 mins till the pork is cooked through.
Tip the drained celeriac back into the pan. Set over a low heat. Cook for 2-3 mins to evaporate off any excess moisture. Add in 2 tbsp of the crème fraîche and squeeze in the mustard. Season. Mash together till smoothish. Cover to keep warm.
Roughly chop the cavolo nero. Wipe the frying pan clean and add 1 tbsp oil. Warm over a medium heat. Stir and fry the cavolo nero for 2 mins till softened and charred. Serve with the celeriac mash and pork chops, with the apricot and sage sauce spooned over.