Begin by making the fish goujons. For these, mix the flour and 600ml water in a bowl, and mix to make a thick batter.
Fill deep-fat fryer or pan one-third full with oil, and heat to 170°C.
Fry the fish, a handful at a time, turning once, before lifting it out onto kitchen paper. Drain on kitchen paper, and keep them warm in a low oven.
To make the pea mash, cook peas, butter, oil and mint in a pan until just tender. Season with salt and pepper, and serve.
To make the rösti potatoes, peel potatoes and grate on a coarse grater or potato ricer into a bowl of cold water. Drain well and divide the mixture.
Prepare a large frying pan with the oil.
Flatten the grated potatoes with a spoon or the back of a fork, and cook over medium heat until golden and crisp. Season well.
Serving Suggestions: Serve the fish with the rösti, and pass a jar of the pea mash.