Cook the potatoes in plenty of salted water until that they are tender. Let cool before peeling and roughly mashing with a fork. Meanwhile, peel and dice the carrots and cook them in salted water for about 10 minutes. Drain and reserve.
Peel the eggs, separate the whites from the yolks and chop both individually. Drain the tuna well (save the oil for another use) and crumble it. Finely chop the onion.
We line a 10 cm diameter plating ring with parchment paper, letting it stand out in height. We put it on a presentation plate and we assemble the salad layered mimosa: potato, mayonnaise, tuna, spring onion, yolks, mayonnaise, carrot, mayonnaise and egg whites.
Remove the ring and parchment paper carefully. Sprinkle the surface with black pepper and we decorate with fresh parsley leaves, quartered cherry tomatoes, lumpfish roe, chopped chives or whatever you like and have on hand.