To begin: Place the mussels on a solid baking tray and into a pre-heated oven steam setting 100 °C for 5-6 minutes until the mussels open.
Remove the skin from the dory fillet/s and portion the fillet/s into finger size pieces. Place the fish fillets on a sheet of baking paper and season with a little salt and extra virgin olive oil. Place another sheet of baking paper over the fillet/s and place on to a perforated baking tray.
Once the mussels have opened remove from the oven and remove the meat fro the shells and set aside. Reserve the cooking liquid in the bottom of the baking tray. To the same tray with the mussel liquid in it add the watercress and place it in the oven steam setting 100 °C for 3 minutes. Dress the mussel meat with a drizzle of extra virgin olive oil and set aside.
Once the watercress has wilted remove it from the oven and change the temperature to 85 °C steam setting and place the dory fillets in the oven for 9 minutes.
Pour the watercress and mussel liquid into a jug and with a stab blender blend on high speed for 1 minute. Add the cream and blend for a further minute. Pass the watercress broth through a fine mesh sieve into a small mixing bowl. Cover the mixing bowl with cling-film and place it in the oven to warm with the fish.
1 minute before the fish is cooked remove the watercress broth from the oven and spoon it into the bottom of a serving bowl. Scatter some mussel meat in the watercress broth and remove the dory fillets from the oven.
Lay 3-4 dory “fingers” in the bowl and top with a little extra mussel meat, drizzle with some extra virgin olive oil and serve.