Cut salmon fillet into thin slices. Mix oil and lime juice and season to taste with the Mediterranean spice. Sprinkle the salmon with it and 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. Pre-heat the oven (electric cooker: 200 °C/circulating air: 175 °C/gas: see "Pre-heating the oven").
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.
For the potato snow, press the hot potatoes half full into the rings by the 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 hot oven for about 5 minutes, the egg yolk should remain liquid.
Cut the remaining salad into fine strips. Boil up the white sauce and stir in the salad strips. Immediately arrange the potato snow with salad heart cream on the salmon and serve.