Drain thoroughly. Cut the cold potatoes in half and scoop out the insides into a large bowl to leave empty skins. Mash the scooped-out potato. Add the crispy bacon mixture, peas and soft cheese.
Peel and cut the celeriac into 1cm chunks and place in a pan. Cover with cold water, add the vinegar and boil until soft. Drain well and pat dry. Heat a tablespoon of the oil in a pan and when hot ...