For the Saffron Mash, peel and chop the potatoes; cover with water, add the garlic cloves and saffron strands. Bring to the boil and cover until cooked.
Drain the potatoes retaining the saffron and garlic. Add 75g of the butter and mash smoothly. Add the cream and 150 ml of the milk and beat until light and fluffy. Season with salt and pepper to taste.
Meanwhile, lay the cod in an ovenproof dish; cover with the remaining milk. Add the onion and bay leaf. Cover and bake for 20 minutes until the fish is firm. Strain off the milk and reserve.
In the meantime, plunge the tomatoes into a pan of boiling water for 30 seconds; refresh in cold water. Peel, quarter, remove the seeds, and roughly chop the flesh.
Turn up the oven to approximately 230 Celsius. Flake the cod into a buttered ovenproof dish. Add the prawns, mussels and tomatoes; sprinkle over the dill.
Melt 25g butter in a pan and add the flour. Cook for 30 seconds; stir in the reserved milk and cook, stirring, until thickened. Season with salt and pepper and pour over the fish.
Spoon the saffron mash over top of the fish mixture covering it completely. Dot with remaining butter.
Bake in the oven for 10-15 minutes or until nicely browned on top.
Serve with crusty white bread and steamed asparagus tips.