First make the shallot confit by sautéing the diced shallots in the butter for 12-15 minutes until they are soft and golden. Then stir in the madeira, vinegar and stock and bring to just under a boil.
Reduce the heat and simmer the sauce slowly until the liquid has reduced to a sauce consistency.
To make the brandade, sprinkle the cod with salt, thyme & garlic and leave for one hour to marinate. Place the cod in a pot with milk and bring to just under a boil, then reduce the heat and simmer the fish for 8-10 minutes until tender. Remove the cod carefully from the milk.
Meanwhile, cook the potatoes in water until soft, then strain and mash. Add the cream and butter and season well and stir in the parsley.
Place the spinach in a saucepan with a splash of water and heat gently until it wilts, strain any excess liquid from the spinach and season with salt and pepper.
Cook the turbot with some olive oil in a hot pan until it is golden, turn over and cook for another 2 minutes.
To serve, place the spinach on a serving dish. Put some cod brandade on top and lay the turbot on top and drizzle with the shallot confit.