Peel, wash and roughly grate the potatoes. Mix with egg yolk, flour, salt, pepper and nutmeg. Heat 3-4 tablespoons of oil in portions in a large coated pan. Fry approx. 12 Rösti from the potato dough for approx. 3 minutes on each side.
Mix mayonnaise and yoghurt. Peel garlic, chop finely and stir in. Season to taste with salt, pepper and 1 tsp. lemon juice.
Halve the avocado and remove the stone. Peel avocado and dice finely. Immediately sprinkle with 1 tsp. lemon juice. Wash, seed and chop the tomatoes. Wash the lettuce and drain well. Mix 2 tbsp. lemon juice, honey, salt and pepper, fold in 2 tbsp. oil.
Carefully mix prawns, avocado, tomatoes, lettuce and vinaigrette. Arrange 3 rösti each. Spread the crab and salad mixture on top and drizzle with some garlic sauce. Add the rest of the sauce.