Cut the pork into 1 1/2 in. (3.5cm) pieces. Heat the oil in a saucepan, add the butter and quickly fry the pork pieces until they are just beginning to brown. Remove them from the pan and drain on kitchen paper.

Add the onion and paprika pepper to the pan and fry for 2 minutes. Remove the pan from the heat, blend in the flour and cook for 1 minute.

Stir in the water, crumbled bouillon cube, sherry and tomato puree, return to the heat and bring to the boil, stirring constantly until the sauce has thickened. Season well with salt and pepper and add the meat. Cover with a lid or foil and simmer for about 40 minutes or until the pork is tender.

At the end of the cooking time, add the whole mushrooms. Blend the cornflour to a smooth paste with the water, add to the pan and bring to the boil.

Just before serving, stir in the soured cream or turn into a warm serving dish and spoon the soured cream on top.

Serve immediately.