Wash the potatoes thoroughly. You can peel them or leave the skin on for extra rustic charm.

Place potatoes in a pot, cover with cold water, add a pinch of salt, and bring to a boil. Cook until tender, about 15-20 minutes depending on size.

While potatoes cook, prepare the herring. Rinse fillets if they seem very salty, then pat dry. Cut the herring into bite-sized pieces.

Drain the cooked potatoes and let them cool slightly. Cut larger potatoes into halves or quarters if needed.

In a bowl, gently combine the cut potatoes and herring pieces.

Pour the kefir over the mixture. If using optional onion and dill, add them now.

Season with a little salt (be mindful of the herring's saltiness) and black pepper. Stir gently to coat everything.

Serve immediately or chill for later. This dish is often enjoyed cold or at room temperature.