1. Preheat the oven to 220°C/425°F/Gas 7. Cut the salmon and cod into large bite-sized pieces and place in a frying pan. Pour over enough water to cover, season and bring to the boil. Cover and simmer for 4-5 minutes until just cooked through. Drain and place in an oven proof dish with the prawns.
2. Blanch the broccoli, drain and add to the fish mixture with the cherry tomatoes.
3. Peel and crush the garlic, beat the egg and mix the mustard with 1 tsp water. Add the garlic, egg, mustard and herbs to the fromage frais and beat until smooth. Season well and pour over the fish mixture, tossing gently to coat.
4. Peel and dice the butternut squash and swede and cook in separate pans until tender. Drain, mash and season well. Spoon the butternut squash over the fish mixture and top with the swede. Bake in the oven for 15-20 minutes until golden. Serve immediately.