In a large pot, heat 1–2 tablespoons of Neutral Oil over medium heat and add diced Smoked Bacon; cook until the fat renders and the bacon starts to brown, about 5–7 minutes.
Add sliced Smoked Polish Kielbasa to the pot and brown briefly with the bacon to develop flavor, about 3 minutes.
Stir in chopped Onion and minced Garlic and sauté until the onion is soft and translucent, about 4–5 minutes.
Pour in enough Water to cover the ingredients by a couple of inches (about 6–8 cups), then add peeled and diced Potatoes, Bay Leaf, a few Allspice Berries, and a pinch of Salt and Ground Black Pepper. Bring to a simmer.
Reduce heat and simmer gently until the potatoes are tender, about 20–25 minutes. Keep the soup at a low simmer so the flavors meld without boiling too hard.
Lower the heat and slowly stir in the Sour Rye Starter to taste—start with a modest amount and add more until you reach the desired tang. Let the soup warm through gently for 5–10 minutes (do not boil vigorously after adding the starter).
While the soup is finishing, hard-boil the Eggs: place in boiling water for 9 minutes, cool, peel, and halve.
Temper the Sour Cream by whisking a few tablespoons of hot soup into it, then stir the tempered cream back into the pot to enrich the broth. Add Dried Marjoram, taste and adjust seasoning with more Salt and Ground Black Pepper if needed.
Ladle the soup into bowls, top with halved Eggs and extra slices of Smoked Polish Kielbasa or a sprinkle of Dried Marjoram if desired, and serve hot with rustic bread.
