Pre-heat your oven to 180C / gas 4.
Cut 4 large rectangular pieces of non-stick parchment paper, roughly 30cm x 25cm.
Bring a pan of water to the boil and cook the potatoes for about 8 minutes, drain.
Take a piece of the parchment and fold in half. Divide the potatoes, pepper and spinach between the parchment paper on one half. Place a cod steak on top then place a slice of lemon on the fish. Season with salt and milled pepper and scatter over the parsley.
Drizzle over the wine and add a dot of butter. Wet the edges of the parchment with water and then seal all the ingredients in - like making a Cornish pasty.
Place the parcels onto a baking sheet and cook for about 15-20 minutes depending on how thick your cod is. Place the en papillote on serving plates so you open at the table.