Bring the double cream to boil on medium heat; add the saffron, set aside for 10 minutes (or as long you need to prepare the rest of the dish).
Heat 0,5 tbsp olive oil with 1 tbsp butter, add the asparagus (excluding the tops) and fry on medium heat for 3 minutes stirring occasionally. Add the heads of the asparagus, season and cook for 1 minute longer; set aside.
Cook the pasta as per the packet instructions (keep a cup of pasta cooking water).
Heat the remaining 0.5 tbsp olive oil and 3 tbsp butter on medium heat, add the chopped shallots and fry stirring for 3-5 minutes till they are golden.
Add the salmon pieces and fry for 2 minutes; then add the prawns and fry for 2-3 minutes longer.
Combine the fish with the asparagus, and saffron cream; heat up, season well and add the cooked pasta. If the dish seems to be too dry add some of the pasta water (if you are not counting calories, you can add some extra butter).