Peel and finely chop the onion. Heat 2 tablespoons of oil in a saucepan and sauté the onion. Add deep-frozen spinach and 5 tablespoons of water, cover and cook over medium heat for about 15 minutes, stirring occasionally. For the béchamel, melt the fat, dust with flour and sauté briefly, stirring continuously. Gradually add 400 ml water and milk, stirring continuously. Bring to the boil, stir in the stock and let everything simmer for about 5 minutes at low heat
Heat 2 tablespoons of oil in a large frying pan. Beat the eggs one by one and let them slide into the pan. Season with salt and fry covered for about 5 minutes until the egg has set. Season spinach with salt, pepper and nutmeg, drain well. Season sauce to taste as well
Grease a high casserole dish (approx. 2.5 litres capacity). Pour some sauce on the bottom and spread. Place lasagne sheets in portions on top in one layer. Spread about 1/3 of the spinach on top (for the first two layers take a little more). Pour the béchamel sauce on top, place the lasagne sheets on top and spread some more sauce on top. Place slices of liver cheese on top and add the fried eggs. Spread about 1/3 of the spinach on top and cover with lasagne sheets. Cover with Leberkäse and spread sauce on top. Put the remaining spinach on top and sprinkle with Gouda. Bake in the preheated oven (electric cooker: 200 °C/ convection oven: 175 °C/ gas: level 3) for approx. 40 minutes until golden brown