tablespoons extra-virgin olive oil, plus extra for drizzling
400g (14oz) celeriac, peeled and cut into 2cm (3⁄4in) cubes
1 onion, finely diced
3 or 4 thyme sprigs
50g (13⁄4oz) shelled cobnuts or hazelnuts, roughly chopped
2 garlic cloves, peeled and grated, plus an extra clove, halved, for rubbing
4–6 sage leaves, torn
1 litre (35fl oz) good-quality, chicken or vegetable stock
1 small bunch Tuscan or curly kale (about 75g/21⁄2oz), tough stem removed, leaves roughly chopped
1 bunch flat-leaf parsley, finely chopped
salt and freshly ground black pepper
toasted or chargrilled bread, for serving
Heat the olive oil in a large heavy-based pan over a medium heat. Add the celeriac, diced onion and thyme sprigs. Cook, stirring regularly, for 5–6 minutes, until the onion is soft but not coloured, then season the celeriac with salt and pepper. Scatter over the chopped nuts, the grated garlic, and the torn sage leaves and stir well. Cook for 1–2 minutes more, then add the stock and bring the contents of the pan up to a simmer.
Cook gently for 8–10 minutes until the celeriac is tender, then add the chopped kale and return to a simmer. Cook for a further 10 minutes, until the kale is tender, then remove the soup from the heat. Add the chopped parsley to the pan, then season well with salt and pepper.
Ladle the soup into bowls and serve with some toasted or chargrilled bread rubbed with a halved garlic clove and sprinkled with flaky salt, then drizzled with your best olive oil.