Prepare the vegetables and eggs: put whole, scrubbed Beet in a small pot and cover with Water; in a separate pot cover whole Potato and Carrot with water; bring both to a boil and simmer until each vegetable is tender (beets 45–60 minutes, potatoes and carrots 20–30 minutes).
While the vegetables cook, hard-boil the Egg for about 9–10 minutes, then cool in cold water and peel.
When cool enough to handle, peel the beet, potato and carrot and grate them on a coarse side of a box grater into separate bowls; finely grate the peeled egg and set aside.
Quick-pickle the onion: thinly slice the Onion and combine in a small bowl with 2 tablespoons White Vinegar, 2 tablespoons Water and 1 teaspoon Sugar; let sit for 10–15 minutes to soften and mellow the bite, then drain.
Prepare the fish: rinse the Salted Herring under cold water to reduce excess salt, remove skin and bones, and chop the fillets into small bite-sized pieces.
Choose a shallow serving dish or ring mold and begin layering: spread the chopped herring evenly as the bottom layer.
Top the herring with the drained pickled onion, then add a layer of grated potato and spread a thin layer of Mayonnaise over it; continue with a layer of grated carrot followed by another thin spread of mayonnaise.
Sprinkle the grated egg evenly over the carrot layer, then cover with the grated beet to form the top colorful layer; spread a final thin coat of mayonnaise over the beets to seal the salad.
Season the top lightly with freshly ground Black Pepper to taste (additional salt is usually unnecessary because of the salted herring).
Cover the assembled salad with plastic wrap and refrigerate for at least 2–4 hours, preferably overnight, to allow the layers to compress and the flavors to meld. Before serving, remove the mold if used, slice into portions, and serve chilled.
