Sift flour into a bowl, add salt and form a well in the middle. Crumble yeast and mix in with a little water to form a dough. Cover and let rest 15 minutes. Then add oil and the remaining water to process into a smooth dough. Cover and let rise another 20 minutes. In the meantime, rinse the potatoes and cut into very thin slices. Peel onion and cut into thin rings.
Divide the dough into four pieces, roll out each piece of dough on a floured surface into a circle. Sprinkle dough with Emmentaler, then cover with the potato slices, onion rings and rosemary, season with salt and pepper and bake in a preheated oven at 220°C about 15 minutes. Then top with Parmesan cheese and bake for another 10 minutes.