• 4 large baking potatoes
• 50g (1¾oz) unsalted butter
• 1 onion, thinly sliced
• 4 garlic cloves, thinly sliced
• 1 small celeriac, peeled and cut into 2–3cm (¾–1¼in) dice
• 1 handful of dried cep mushrooms
• 100ml (3½fl oz) double cream
• 100ml (3½fl oz) whole milk
• 1 tsp dried seaweed flakes (optional)
• 1 handful of flat-leaf parsley, leaves picked and chopped
• 1 handful of grated cheddar cheese
• Flaky sea salt and freshly ground black pepper

Heat the oven to 190°C/170°C fan/375°F/gas mark 5.

Wash the potatoes, then sprinkle them with a little salt. Place them on a baking tray in the middle of the oven for 1–11⁄4 hours, or until cooked through. Remove from the oven and, when cool enough to handle, halve them and scoop out as much hot flesh as you can, without tearing the skins. Place the flesh in a bowl, then return the hollow skins to the oven for 10 minutes to crisp up. Remove from the oven and set aside.

While the skins are crisping, heat a heavy pan over a medium–low heat. Add the butter and, when it’s melted and bubbling, add the onion, garlic, celeriac and dried ceps and season with some salt and pepper. Cook, stirring regularly, for 25–30 minutes, or until the celeriac is nice and soft (if it begins to catch on the bottom, lower the heat and add a dash of water – that’ll stop the problem). Add the cream, milk, potato flesh, seaweed flakes (if using) and parsley. Season to taste and stir to combine.

Pile the celeriac mixture into the crisped potato skins. Place the potato halves back on the baking tray, if necessary, and scatter over the cheese. Return the filled potatoes to the oven for 12–15 minutes, or until the fillings are nice and hot in the middle. Serve sprinkled with flaky salt and with a dressed green salad on the side.