How to Make It
In a small skillet, toast the caraway seeds over medium heat, stirring until fragrant, about 2 minutes. Finely grind the seeds in a spice grinder.
In a large pot, melt the butter. Add the sausage and cook over moderate heat until browned all over, about 5 minutes. Transfer the sausage to a plate, cover and refrigerate.
Add the escarole, carrots, celery, onion, fennel, garlic, thyme and ground caraway seeds to the pot and cook over moderate heat, stirring occasionally, until the vegetables start to soften, about 10 minutes. Add the ham bone and broth and bring to a boil. Add the peas, cover partially and simmer until the peas are tender, about 1 hour.
Gently mash some of the peas to thicken the broth. Thinly slice the sausage, add it to the soup and simmer until the sausage is cooked through, about 10 minutes. Season the stew with sea salt and white pepper. Serve with white vinegar, hot sauce and bread.