Potato, celeriac and apple gratin

Method

1. Preheat the oven to 200°C/fan180°C/gas 6. Very thinly slice the peeled potatoes using a mandolin, if you have one, or in a food processor. Do the same with the celeriac.
2. Put the cream, milk and garlic in a non-stick pan over a medium-low heat. Add the potatoes and celeriac and simmer for 10 minutes, gently stirring, until tender.
3. Spoon half the potatoes and celeriac into a greased 1.5-litre ovenproof dish, then season. Quarter, core and thinly slice the unpeeled apples and arrange over the potato. Top with the remaining potatoes and celeriac, season and dot with butter.
4. Bake in the oven for 30-35 minutes, until golden and bubbling