Wash beans well and pick over for stones and debris. Soak beans with kombu in plenty of fresh cold water overnight or at least 6 hours. This can be done in a covered container or in a pot (I use the same pot for soaking as for cooking the soup) on a countertop. Refrigerate if your kitchen is warm.Just before you begin cooking, drain the beans into a colander. Heat the oil over medium heat in a large heavy-bottomed pot, and add the onion and garlic. Cook until softened, about 8-10 minutes.Add the beans and stock to the pot and raise the heat to high. You can add the kombu to the pot, if you like for additional alkalinity. Bring soup to a boil, cover, then lower to a simmer. Cook for 1 hour.Add the potato, sea salt and (optional) rosemary. Cover and simmer for 30 minutes. Test the beans for tenderness. If they’re not done, continue to simmer until they’re tender. Once beans are tender, you can puree the soup to your desired consistency or leave chunky. Remove the kombu and sprig of rosemary before pureeing.Stir in the escarole and cook until wilted. Serve with grated cheese, if desired.