500 ml (17 fl oz) good-quality, boiling vegetable or lamb stock
3 parsnips, cut into chunks
1 small celeriac, peeled and cut into chunks
3 carrots, sliced 1 cm (½ inch) thick
2 leeks, thickly sliced
1 tablespoon chopped rosemary
2 tablespoons olive oil
salt and pepper
finely chopped curly parsley, to garnish (optional)
Cook the potatoes in a large pan of salted boiling water for 8–10 minutes, until just tender. Drain well and set aside to cool slightly.
Meanwhile, melt the butter in a large saucepan or flameproof casserole dish and cook the onion and garlic over a medium heat for about 5 minutes, until slightly softened and coloured.
Pour in the stock and add the prepared vegetables and rosemary. Season with a pinch of salt and pepper, then cover and simmer over a medium heat for 15–20 minutes, until the vegetables are tender.
Once the potatoes are cool enough to handle, slice thickly. Heat the oil in a large, nonstick frying pan and fry the potatoes over a medium heat for 10–12 minutes, turning occasionally, until crisp and golden. Drain on kitchen paper.
Ladle the vegetable hotpot into shallow bowls, top with the potato slices and serve immediately, garnished with freshly chopped parsley, if desired.