Crushed chopped onion and fry it in hot sunflower oil. Add the flour, chopped ham, spices. Dilute the roux with milk. Once the mixture boils, remove from heat and add the yolks. In the sauce put already cooked potatoes - sliced. Mix everything well and transfer it in a greased baking pan. Sprinkle with cheese and bake in the oven for 30 minutes.