Boil eggs, carrots and potatoes (both not peeled). Let the cool and peel all of them. Dice potatoes and carrots into small cubes. Separate egg yolks from egg whites and dice the egg white. Keep everything separate from each other. Chop an onion. Strain smoked canned sprats from the oil (you can keep part of it) and mash them with a fork.
Put half of sprats in the serving dish, cover with half of chopped onion. Cover with half of chopped egg whites and spread mayonnaise on top. On the mayonnaise layer, spread half of diced potatoes and a layer of diced carrots. Spread another layer of mayonnaise. You can also drizzle the sprats oil on the potatoes for extra flavor.
Repeat the layers. On the last layer of carrots, spread a layer of mayonnaise and cover with grated yolks. Cover the dish and set in the fridge for a fer hours. Serve cold, with rye bread, garnished with spring onions.