Cut the courgette, carrot and turnip into small even shapes and trim the leek, using the white part only. Blanch the vegetables.
Fillet the John Dory, leaving the tail and one bone intact, so as to keep both fillets on the fish. Place the spinach on the fillets, then sandwich the fish back together with the salmon mousse. Encase the fish with caul fat.
Steam the fish for 20 minu