Boil the beetroot (1 pc.) and chop it with a food processor.
Boil potatoes (1 pc.) in salted water and puree. Add boiled milk and butter (30 gr.) to the mashed potatoes. Then finely chop the parsley and add to the mashed potatoes.
Add mayonnaise to the chopped beetroot (1 tablespoon without a slide), salt and pepper with ground black pepper to taste. Mix the beetroot minced meat.
Cut the herring into fillets without skin and bones, cut into portions. You can buy ready-made fillets.
Cut the black bread into a sandwich ring.
Finely chop the green onion.
Put mashed potatoes and mashed boiled beets on portioned slices of bread using a pastry bag. For each serving, put slices of herring with potato-beet puree. Sprinkle the structure with finely chopped green onions on top.