Whizzed-up breadcrumbs from the end of a loaf can be stored in the freezer. As long as they’re very dry to begin with, you don’t need to defrost them. Double up the bake quantities for future lunches or dinners.
Preheat the oven to 160C/140C fan/gas 3. Cut four 1.5cm thick slices from the celeriac, trimming them into 10cm circles. Sprinkle with sea salt and a few leaves of chopped thyme. Leave to one side for 15 minutes, then wash off the salt with cold water. Lay on a baking sheet and bake for 15 minutes, until soft but not coloured.
Meanwhile, chop the rest of the celeriac (including trimmings) into cubes and cook in boiling salted water until very soft. Drain, add the butter and purée with a hand blender until very smooth. Season and rub through a sieve to make it really silky.
Heat a heavy-bottomed frying pan until very hot. Season the trout and cook it skin side down until golden, turning it carefully with a metal fish slice.
Transfer to a baking sheet and finish cooking in the oven (still at 160C/140C fan/ Gas 3) for four minutes.
Allow to rest on a warm plate for five minutes while you finish the rest of the dish.
Heat two tablespoons of oil in a frying pan. Add the slices of celeriac and cook on both sides until golden. Keep warm.
Cut the pak choi in half lengthways (remove the outer leaves and keep for another dish, such as the salad, right). Cook cut side down in the pan, turning once it has a good dark colour, and cooking for another minute on the outside.
Reheat the purée and warm four plates. Put a slice of celeriac on each plate and top with the trout and pak choi, with a dollop of celeriac purée at the side. Drizzle with the olive oil.
Cut the leaves from the pak choi and finely slice the stems. Cut the leaves into three. Thinly slice half an apple. Put everything in a bowl.
Whisk together the dressing ingredients and mix into the apple and pak choi.