Sauté the onions in olive oil until translucent, then sauté the tomatoes + garlic briefly.
Add the tomato sauce and season with pepper, salt and harissa. Bring to the boil briefly.
Place the potato slices and sauce in layers in a baking dish. The last layer should be sauce. Sprinkle parsley on top. Then spread the sheep`s cheese on top. Season again with pepper, salt and paprika.
Put the casserole in the preheated oven (middle rack) for about 1/4 hour at 200 degrees and bake it over the top. It`s ready when the sheep`s cheese has melted a little and is slightly golden.
Tip: The jacket potatoes from the previous day are best, as they are easier to cut than freshly cooked ones. The casserole is also a good idea for using leftovers.