Preheat the oven to 180C/160C Fan/Gas 4. Wash the spinach in cold water, then drain in a colander. Stir-fry for 3-4 minutes in a wok. Tip back into the colander and press with the back of a wooden spoon to press out as much liquid as possible. Once cool, squeeze with your hands to extract more liquid. Put in a bowl.
Heat 15g butter in a pan then add the crushed garlic and cook for a minute. Add to the spinach and season. Mix well.
To skin the plaice, put on a board, skin-side down, and hold in place at the tail end. Insert a sharp knife at a slight angle between the skin and flesh and, moving away from yourself, cut the skin from the flesh with a slight sawing movement.
Spread the fillets, skin-side down, with the crab. Share the spinach between them and fold in three. Put in a greased ovenproof dish, skin-side down, and dot with the rest of the butter. Cover the dish with foil and bake for 15-20 minutes or until the fish flakes easily.
Put the wine in a pan and boil until reduced by half. Remove from the heat, add the stock and any fish juices. Mix the cornflour with 2tbsp cold water and stir into the pan. Bring to the boil, stirring constantly, and simmer for a minute.
Add the creme fraiche and parsley and serve with the plaice and broccoli.