Wash the potatoes and cook covered for about 20 minutes. Quench, peel and let cool down.
Peel and chop the onions and garlic. Sauté garlic and half onions in hot oil. Add spinach and 5-6 tablespoons of water. Cover and simmer until defrosted. Drain and season.
Finely dice the ham. Wash the tomatoes. Tomatoes.
and cut the potatoes into slices.
Fry the rest of the onions in hot fat. Add flour and sweat. 1⁄2 Stir in l water, milk and stock, bring to the boil. Simmer sauce for about 5 minutes. Whisk egg yolk and some hot sauce and stir into the sauce (do not boil any more!).
Grate cheese, stir in half. Season to taste.
Spread a thin layer of sauce in a greased casserole dish. Potatoes, ham,.
Alternately layer spinach and tomatoes with some sauce. Finish with sauce and remaining cheese. Bake in a hot oven (electric cooker: 200 °C/circulating air: 175 °C/gas: level 3) for 45-50 minutes.