Preheat the oven to 220C/450F/Gas 7.
For the cod, heat a frying pan until hot, add half the butter and all the spinach. Cook until the spinach is just wilted. Transfer the spinach to a colander and press remove any excess water. Allow to cool slightly and chop finely.
In a bowl mix the chopped spinach with the parsley, breadcrumbs and grated cheese.
Heat a large ovenproof frying pan and add the remaining butter. When the butter has melted, add the cod, skin-side down. Fry for 2-3 minutes, or until the skin is crisp.
Top the cod with the spinach and breadcrumb mixture, and place in the oven for 5-7 minutes.
For the white wine sauce, heat a frying pan and add the butter. Once melted add the shallots and fry for 2-3 minutes. Add the garlic and cook for a further two minutes. Pour in the wine and stock, then bring to the boil. Cook until the volume of the liquid has reduced by half. Remove from the heat and stir through the cream.
For the fennel salad, mix the fennel, carrots, cucumber, red onion, dill and lemon juice in a bowl until well combined. Season to taste with salt and freshly ground black pepper and drizzle with olive oil.
To serve, divide the fennel salad between four serving plates and place a fillet of cod on top. Pour the white wine sauce over the cod.