This comforting yet luxurious gratin can be served as a main course or side-dish. Celeriac is often served raw in a mustardy sauce as celeriac rémoulade, and this dish uses the same flavour combination. Include the ham or not, as you prefer. You can also grate over Parmesan or Cheddar for extra flavour before it goes in the oven.
- 300g/10½oz potato (1 large baking potato), peeled or scrubbed and cut into 1cm/½in slices
- 2 banana shallots, finely sliced
- 3 tbsp finely chopped flatleaf parsley
- 350g/12oz peeled celeriac (about ½ large one), finely sliced
- 50–100g/1¾–3½oz air-cured ham, such as Parma or Serrano, thickly sliced (optional)
- 1½ tbsp capers, rinsed well and drained
- 300ml/10fl oz full-fat crème fraîche
- 500ml/18fl oz full-fat milk
- 1½ tbsp Dijon or grainy mustard
- 1 garlic clove, finely chopped
- sea salt and freshly ground black pepper
- Preheat the oven to 200C/180C Fan/Gas 6.
- In a large bowl, mix the potato, shallots, parsley, celeriac and ham, if using. Add the capers and season with pepper and a pinch of salt. Tip the mixture into an ovenproof dish (approximately 30cm/12in square and not too deep).
- Heat the crème fraîche and milk in a small pan. Stir in the mustard and garlic and season with half a teaspoon flaky sea salt and pepper. Bring to a gentle boil, then pour over the gratin. It won’t cover the vegetables – that’s fine.
- Bake for 1 hour 15 minutes, or until the vegetables are tender. Cover the top with foil if it is getting too brown. Leave to sit for 5 minutes before serving.