Add fish to pan of cold water, bring to the boil, reduce heat, cover, simmer few minutes or until fish is just tender. Remove fish from pan, combine in bowl with chopped prawns, mussels and tasty cheese. Melt butter in pan, add flour, stir until smooth cook, stirring for 1 minute. Gradually stir in milk and sour cream, stir constantly over heat until mixture boils and thickens, remove from heat, stir in shallots and lemon juice, stir in seafood mixture, cool to room temperature. (Note: I used crab meat not mussels). Brush a sheet of pastry with extra butter, top with another sheet of pastry, brush with butter, sprinkle with about a tablespoon of the combined breadcrumbs, parmesan cheese, parsley and mustard. Repeat buttering between each layer of pastry and sprinkling with breadcrumb mixture between every second layer, until half the pastry has been used. Place half the seafood mixture along the long side of the pastry, leaving a 5cm border. Fold sides in, rollup like a Swiss roll. Brush all over with butter. Repeat with remaining ingredients to make another strudel. Place strudels onto a large oven tray. Bake in moderate oven for 30 minutes. Serve hot with sauce. (Remember, you can prep the strudels in the morning and leave them in the fridge till you are ready for them.)

Heat butter and garlic in pan,, lemon juice, lemon rind and saffron; stir constantly over heat until mixture boils and thickens.