Preheat the oven to 220°C, 200°C Fan, Gas Mark 7. Put a tray into the oven to heat up. Put the potatoes into a pan of cold, salted water and cover with a lid. Bring to the boil then as soon as the water is boiling, turn the heat down and simmer for 5-6 minutes. Drain in a colander and shake well to roughen up the edges.
Put 2 tablespoons oil into a bowl and tip the potatoes into it. Toss well and season with salt. Tip into the roasting tray. Roast for 15 minutes.
Put each piece of cod onto the baking sheet and put a slice of shallot on top of each.
Toss the potatoes around, then return the tray to the oven and continue to roast for 15 minutes.
Stir the chives, parsley and capers into the butter and season well. Cook the peas until tender in a pan of boiling salted water and drain well. Add a little of the mixed butter.
Take the tray out of the oven and divide the potatoes and fish between two plates. Spoon the remaining butter onto each fish fillet and serve with the peas and lemon wedges.
350g fluffy potatoes, such as Maris Piper or King Edward, peeled and cut into chunks
2 tablespoons rapeseed oil
2 x 150g cod fillets
2 thin slices of shallot
½ lemon, cut in half to make two wedges
For the herb butter
1 tablespoon freshly chopped chives
1 tablespoon freshly chopped parsley
1 teaspoon capers
A knob of butter