The next day, peel and finely dice the onions and garlic. Peel or clean and wash vegetables. Cut the carrots into slices, finely dice the celery. Wash the rosemary and pat dry.
Heat 1 tablespoon of oil in a large saucepan. Sauté onions, garlic, vegetables and 1 sprig of rosemary while stirring. Add the beans with the soaking water and bring to the boil. Cover and simmer for 1.5-2 hours, until the beans are soft.
Cook the tagliatelle in boiling salted water for about 6 minutes. Drain.
Stir the broth into the soup. Remove the sprig of rosemary. Lift out about half of the beans and vegetables. Puree the soup. Put the pasta, beans and vegetables back into the soup and heat. Season to taste with salt and pepper. Roughly chop the rest of the rosemary.
Serve the soup, sprinkle with rosemary and drizzle with 1 - 2 tablespoons of olive oil.