Polish-style Sour Rye Soup
To make the sour rye, place the rye in a mason jar and pour in 400 ml (about 1 3/4 cups) warm water. Cover the jar with parchment paper and secure with string or a rubber band. Poke several small holes in the paper with a needle. Let ferment 2 to 3 days at room temperature.
Peel the carrot, onion, potato, and garlic. Cut all the vegetables into small dice. Cut the pancetta into small cubes.
In a soup pot, heat 1 tablespoon oil. Add the bacon and and onion sauté until crispy. Remove the pancetta and onion with a slotted spoon, letting the fat drain back into the pan. Set aside.
Add the carrot, potato, and garlic to the fat and drippings in the pot and sauté briefly. Deglaze with the broth. Add the marjoram. Cover the pot and simmer gently over medium heat about 20 minutes and then purée the soup. Stir in the sour rye and simmer for another 5 minutes. Stir in the sour heavy cream and remove from the heat. Season the soup with salt and pepper.
To serve, ladle the soup into heated soup plates and sprinkle with pancetta-onion mixture and parsley.