Serves 6 generously
800g celeriac, peeled & quartered
800g medium potatoes, halved & unpeeled
3 tablespoons olive oil
salt & ground black pepper
you will need a deep-sided 25cm non stick frying pan
Place the celeriac and potatoes in a large saucepan, cover with cold water and bring to the boil. Turn off the heat, cover with the pan lid and set aside for ten minutes. Drain well and leave to cool. Grate the celeriac and potatoes into a bowl, season and mix together.
Melt half the butter with one tablespoon of oil, coating the base and sides of the pan. Add the celeriac mixture and gently press down to form a large cake. Cook for 5 minutes over a high heat. Pour 1 tablespoon of olive oil around the edge of the pan and gently shake to avoid the rosti from sticking.
Reduce the heat to medium and cook for 10 minutes, shaking the pan often. Take a slightly larger plate and place it on top of the pan. Carefully invert the rosti onto the plate.
Add the remaining butter and oil to the pan and return the rosti, cooked side up. Cook for a further 10 minutes.
Serve with a dozen Cumberland sausages and a selection of your favourite mustards.