Remove head and bones and sauté in olive oil with the onion celery, garlic roughly chopped, than cover with water bring to the boil and simmer for 45 minutes. Chop the spring onion, fennel and sauté in olive oil on low heat without coloring. Meanwhile slice the fish fillet and toss it in. Once cooked add the saffron and keep tossing, pour in the wine, bring to the boil than add the some fish stock and simmer. Finally add the cream, butter and simmer for a few more minutes, toss in the cooked pasta, spinach and season.