Peel the celeriac, cut it into 3-4cm wedges and finely slice. Heat 3 tablespoons of the olive oil in a large saucepan over a medium heat and fry the shallots for a few minutes until softened, stirring frequently. Add the celeriac, season and continue to fry for 7-8 minutes, stirring, until golden, then stir in the cumin.
Add 75ml kettle-hot water, cover and cook over a low heat for 5 minutes more, until tender.
Whiz the hazelnuts in a food processor for 5 minutes or until they turn into a thick paste; scrape down the sides from time to time. Add the pan contents, the garlic, the lemon juice and remaining oil; whiz again to combine. Leave to cool for 15 minutes; add the yogurt, whiz again and season.
Transfer the mixture to a bowl. Drizzle with oil, dust with paprika and scatter over a little parsley, before serving with crudités, toasted pitta, olives and/or pickled chillies.