Fillet the fish and use to head and bones for the stock. In a medium pan sauté in olive oil the fish bones, onion, peppercorns and half the fennel until softened. Add the 1/2 glass white wine than 2 glasses of water bring to the boil and simmer. Add the bay leaves and allow 45 minutes to infuse on low heat. Remove the fish skin, and dice finely the fennel and spring onion, than sauté on very low heat until the fish starts to flake. Strain the stock and add 1 cup together with the saffron and bring to the boil. Lower the temperature adding a few more stock and keep simmering, add the fresh cream and reduce by half. Meanwhile boil the pasta separately drain and add to the sauce, simmer add the spinach, season and toss. Allow some time on low heat tossing continuously to allow pasta absorb some of the sauce flavors than serve.