Celeriac and potato dauphinoise recipe

Preheat the oven to 180°C/fan160°C/gas 4. Lightly butter a large ovenproof dish. Peel and finely slice the potatoes. Peel the celeriac, quarter, and finely slice. Layer the vegetables randomly in the dish.

Put the remaining ingredients in a large pan, bring just to the boil, then season. Pour into the dish, cover with foil and bake for 40 minutes. Check halfway through, and pat down with a spatula. Uncover and bake for a further 10-15 minutes, until golden. Stand for 10 minutes before serving.