Shred the wedges of celeriac using the grating disc of a food processor, or thinly slice using a sharp knife. Put into a pot of boiling water with half the lemon juice, cook for 5 minutes until tender, then drain well and put into a large bowl. Shred the cabbage in the same way as the celeriac, then add to the bowl with the celeriac, along with the onion.
In a screw-top jar, shake together the ingredients for the dressing and season to taste. Spoon two-thirds of the dressing over the celeriac, cabbage and onion and toss lightly. Set aside.
Heat a small non-stick frying pan over a moderate heat, dry-fry the walnuts for 2 minutes, stirring, then take off the heat and reserve. Cut the Edam into matchsticks. Core the apple, cut it into thin slices, then put on a plate and sprinkle with the rest of the lemon juice to prevent it discolouring.
Just before serving, toss the Edam, apple slices and toasted walnuts into the salad. Spoon over the rest of the dressing, toss and serve immediately.
Recipe Notes
Each serving: 13 g protein, 26 g fat of which 6 g saturates, 14 g carbohydrate, 10.5 g fibre, 354 Calories