Leave the sausage to simmer in warm water for about 45 minutes.
Cut the kale leaves from the stalk and roughly chop. Parboil in a good amount of boiling salted water for 5 minutes. Drain in a sieve and refresh with cold water. Carefully squeeze out any excess water.
Peel the potatoes and cut into thin 5 mm slices, cook for about 5 minutes until they are just beginning soften. Peel the pears, cut into pieces. Place the potatoes and pears in a gratin dish and distribute the kale over the top.
Finely grate the Emmentaler AOP. Whisk the eggs with milk, quark, mustard and 100 g cheese. Season with salt and pepper and pour over the kale. Bake in a 180 degree hot oven for 15 minutes.
Roughly chop the walnuts, mix with the remaining cheese and put on top of the gratin. Dot with flakes of butter and bake for a further 15-20 minutes.