Put the dried porcini in a bowl and pour over 250ml boiling water. Once the mushrooms have rehydrated, strain off the liquid and use to make a beef stock with the stock cube. Set the mushrooms aside.

Season the steaks well. Heat half the butter in a frying pan until sizzling, then cook the steaks for 8-10 mins, turning every minute or so, until golden brown on each side. Set aside to rest.

Heat the rest of the butter in the pan and fry the onion for 8-10 mins, until starting to caramelise. Add the porcini and chestnut mushrooms and cook for 5 mins, then add the garlic and paprika and cook for another minute. Stir in the vinegar and simmer for 1 min, then add the stock, bring to the boil and simmer for 5 mins. Reduce the heat and stir in most of the soured cream, until hot but not simmering. Season to taste, then add the mustard and most of the parsley.

Thickly slice the steak, then add to the pan along with any juices. Drizzle with the remaining soured cream, then scatter with the rest of the parsley and a little more paprika. Served with mashed potatoes.