Soak the beans overnight. Finely dice onions and garlic and sauté in olive oil. Drain the beans and cook with the wine, milk and cream for 45-60 minutes, until the beans give way under pressure. Puree the soup, pass through a sieve and, if necessary, top up with stock and cream, season.
Place the Serrano ham on a baking sheet lined with baking paper and sprinkle with brown sugar. Let it dry in the slightly open oven at 50 - 60 ° until you can break it (this can take 2 - 3 hours, depending on the ham!). Cut or break into small pieces.
Cut the mushrooms into leaves, cut the spring onions into oblique pieces 1-1.5 cm long and fry. Divide the soup on plates and garnish with the mushrooms, spring onions, ham, lemon juice and truffle oil.