Slice the celeriac into thin rounds. Bring a pan of salted water to the boil, then cook the slices until al dente. Set aside

Cut the lemongrass stick in half and lightly crush with the back of a knife. Peel the apples, remove the core and cut into cubes

Add the apple cubes to a pan with the the butter, sugar and lemongrass, and simmer until the apple is soft. Remove the lemongrass and mash the apples to a coarse purée

Preheat the oven to 200°C/gas mark 6. Place the chopped cobnuts on a tray and roast until dark brown, this should take about 10–12 minutes

Transfer to a small saucepan and add the milk. Bring to the boil and leave to infuse for 20 minutes. Season with salt and set aside

When ready to serve, add a little butter to a frying pan and fry the celeriac rounds until lightly golden. Warm through the cobnut milk and blend with a hand blender to create a foam

Season the plaice fillets with salt and pepper. Heat the butter in a frying pan until it it foaming and add the fish. Cook until golden brown on each side

To plate, place the fish alongside a few slices of celeriac on each plate. Top with a spoon of the apple purée and some of the cobnut foam