Parsnip and mushroom rösti

1. Preheat the oven to 200˚C, gas mark 6. Put the dried mushrooms in a small, heatproof bowl and just cover with freshly boiled water. Set aside for 10 minutes. Meanwhile, put 1 tbsp oil in a 20cm non-stick ovenproof frying pan and set over a medium heat. Add the onion and a pinch of salt and sauté for 7-8 minutes.

2. Coarsely grate the parsnips and potatoes; toss with the lemon juice. Tip into a clean tea towel and firmly squeeze out over a sink to remove any excess liquid. Tip into a bowl and add the cornflour and sautéed onion; season. Drain the mushrooms well, squeezing out any excess liquid (freeze the soaking water in an ice cube tray, to use in stocks and soups). Chop and add to the parsnip mixture. Stir well to combine.

3. Wipe out the frying pan with kitchen paper. Add 2 tbsp oil and set over a high heat for 30 seconds. Spoon in the rösti mixture, flattening it down firmly, especially at the edges. Turn the heat down to low-medium and cook for 10 minutes, releasing the edges with a spatula once golden. Using a tea towel, put an upside-down plate over the pan, then flip to turn the rösti out. Add the remaining 1 tbsp oil to the pan and slide the rösti back in. Fry for 10 minutes, then bake for 10 minutes, until deep brown and sizzling. Flip the rösti onto a board and quarter it. Quickly top each quarter with crème fraîche, watercress and mackerel (or a poached egg and some feta, to keep it vegetarian), plus a lemon wedge.