Method

1. For the rösti, squeeze the grated potato out into a clean tea towel until dry, then place into a bowl.

2. Place the egg yolk and yoghurt into a separate bowl and whisk together. Add the grated potato and season well with salt and freshly ground black pepper.

3. Melt the butter in a small frying pan. Add the potato mixture to the pan, pressing it down into a disc shape in the pan. Cook over a medium heat until golden brown underneath, then turn the rösti over and cook the other side until golden-brown.

4. For the liver, heat a griddle pan until smoking. Drizzle the griddle pan with one tablespoon of the oil, then add the calves' liver and griddle for 3-4 minutes on each side, or until completely cooked through. Remove from the pan and leave to rest in warm place.

5. Add the remaining half tablespoon of oil to a frying pan and add the sage leaves. Fry the sage for 1-2 minutes, or until crisp.

6. To serve, place the rösti into the centre of a plate and place the liver on top. Garnish with the sage leaves.