Cook carrots, potatoes and eggs until done, cool and peel. Coarsely grate carrots and potatoes separately. Finely chop greens; reserve some sprigs. Finely chop onion and splash with hot-boiling water. Season it with sugar, salt, black pepper and vinegar. Hard-boil eggs and separate the whites from the yolks. Finely chop the whites and mix with greens. Fine grate yolks. Take the sprats out of oil, pat them dry with a paper towel and mash with a fork. Lay sprats and onions with layers in a transparent salad bowl, coating each one thoroughly with mayonnaise. Continue to lay the layers, coating again with mayonnaise: chopped egg whites, then grated carrots and potatoes. Coat the top layer with mayonnaise too and sprinkle with chopped greens. Pour the grated boiled yolks in the center, having receded from the edge for 2-3 cm.