Cut salmon fillet into thin slices. Mix oil and lime juice and season to taste with the Mediterranean spice. Sprinkle the salmon with it, cover and let it simmer cold for at least 30 minutes.
Peel, wash and chop the potatoes. Cook in salted water with 2 tablespoons of butter for about 20 minutes until soft. Drain and let it steam
Clean and wash the lettuce hearts and remove 4 small leaves. Put the rest of the lettuce aside. Grease 4 starter rings (alternatively small bowls or cups) with butter and place in a flat ovenproof dish. To make the potatoes, press the hot potatoes half full into the rings with a potato press. Place 1 small salad leaf on each of the potatoes and place 1 egg yolk on each. Then press the remaining potatoes on top and press them down very carefully. Add 1 teaspoon of butter on top of each. Cover with aluminium foil and bake in a preheated oven (electric cooker: 200 °C/ convection oven: 175 °C/ gas: see manufacturer) for about 5 minutes, the egg yolks should remain liquid.
Bring 150 ml white sauce to the boil. Cut remaining salad into fine strips. Stir into the white sauce. Immediately arrange the potato puree with salad heart cream on the salmon and serve