1. Preheat the oven with a pan inside to 200C. Boil the potatoes whole in heavily salted water until they are three-quarters cooked. Put the potatoes aside and let them cool for five minutes.

2. Finely grate the potatoes.

3. Place a large, heavyset frying pan on high heat. Add the butter and olive oil to the pan. Press the grated potato into the frying pan, making a large round disc. Season with salt and pepper and cook for 10 mins, or until the potato is golden on the underside and around the edges.

4. To finish, place in the oven for five minutes, or until the top is golden brown. Remove the pan from the oven. To serve, place a large wooden chopping board or serving platter over the top of the frying pan. Holding the frying pan in one hand and the platter in the other, flip it over to remove the rosti from the frying pan. This leaves the crispy golden side of the rosti facing upwards.

5. Then, line a tray with baking paper. Lay the trout on the tray and heavily season it with flaked salt and pepper on both sides. Place in the oven and bake for 12-15 mins. Pick some of the pink flesh off the trout and scatter it over the rosti. Using a large spoon, evenly distribute the creme fraiche over the top of the rosti. Sprinkle on the dill. Zest the lemon over the top, and add half the juice. Season well with flaked salt and pepper.

Serve with butter lettuce, dill and radish salad.

If you like this recipe, try our salt-baked trout with sage butter sauce and dill potatoes.

Tip: When grating the boiled potatoes, be sure to make long, firm strokes. This will give you long, thin strings of potato, which is much niceer to eat. Short, little strokes will make it turn out like a mash.