Ingredients
For the mayonnaise (makes 300ml/0.5pt):
2 egg yolks
2 tsp white wine vinegar
1 tsp Dijon mustard
pinch of caster sugar
300ml/0.5pt olive oil

For the salad:
8-10 walnut halves
1 head celeriac
4 russet apples, cored
1 celery heart, leaves picked
salt and pepper

Method
1. To make the mayonnaise, simply place the egg yolks, white wine vinegar, mustard and sugar in a processor or liquidiser and blend to combine. With the motor still running, gradually add the olive oil in a slow and steady stream until all is combined and the mayonnaise has thickened. Season to taste. (Store the mayonnaise in a screw top jar in the fridge).
2. To make the salad, place the walnuts in a small pan and cover with cold water. Bring slowly to the boil and drain. Peel the skin from the nuts with the help of a skewer.
3. Peel the celeriac and cut into large manageable chunks. Using a mandolin, julienne the celeriac pieces into thin strips. Place them immediately into a large bowl with the lemon juice and just enough water to cover. Deal with the apples in exactly the same way.
4. Drain the apples and celeriac and toss them in enough mayonnaise to combine. Season to taste and pile into the centre of a large serving bowl. Scatter the walnuts and celery heart leaves over and serve.