Peel the potatoes and cut them into cubes. Rinse them thoroughly in cold water.
Put the potatoes in plenty of cold water – without salt – bring to the boil and cook until tender.Meanwhile, prepare the stew.
Heat the stew through, ideally in an ovenproof frying pan – that saves you extra washing-up.Add extra cooked vegetables if the stew needs more substance. Adjust the consistency too, with a little milk or stock, for example – or with a little cornflour if it is too runny.The stew should have the consistency of a shepherd's pie filling.
Add the peas and season the stew to taste with salt and freshly ground pepper.
Drain the potatoes, reserving a little of the cooking water, and mash them. I use a potato masher, but you can also use a whisk.
Add the butter and crème fraîche and stir well into the hot mash. Season to taste with salt and adjust the consistency with a little of the cooking water if needed.
Spread the mashed potato over the top of the stew. Rough up the surface with a fork if you like, and make sure the mash goes right to the edges.
Bake in a preheated conventional oven at 200°C for about 30–40 minutes – if it needs more colour, turn the oven up to 230°C for the last 10 minutes or so.
Let it rest for about 10 minutes before serving – top with finely chopped parsley if you like.