Melt the butter, add the egg yolk, Styrian Pumpkin Seed Oil P.G.I. and water and mix well. Add the flour and combine until it is a smooth dough. Set aside. Meanwhile peel the potatoes and cut into thin slices. Sauté the chopped onion until golden brown, add the potato slices and sauté for a short time. Season and set aside. Preheat the oven to 230°C. Roll out the dough to a thin square on a floured surface. Put the cooled potato onion mixture on the dough and roll up to two rolls. Put the rolls on a baking tray, brush with beaten egg and bake until light brown. Let cool before serving. Tip: Serve the slightly warm slices with fresh  green salad.