Ingredient:
60 g (2 oz) butter, plus extra for greasing
1 onion, sliced
2 garlic cloves, crushed
1 kg (2 lb) floury potatoes, thinly sliced
375 g (12 oz) celeriac, peeled and thinly sliced
300 ml (1/2 pint) single cream
150 ml (1/4 pint) milk
250 g (8 oz) ricotta cheese
3 tbsp snipped fresh chives
Salt and black pepper
2 tbsp fresh breadcrumbs
3 tbsp grated Parmesan cheese, plus extra to serve

Method:
Melt the butter in a frying pan, add the sliced onion and crushed garlic, and cook gently, stirring occasionally, for 3-5 minutes until softened but not coloured. Lightly butter a large gratin dish.

Arrange the potatoes, celeriac, and the onion mixture in layers in the prepared gratin dish, finishing with a neat layer of potatoes.

In a large bowl, combine the cream, milk, ricotta cheese, and chives, and season with salt and pepper. Beat well together, then pour over the vegetables.

In a small bowl, combine the breadcrumbs and 3 tbsp grated Parmesan cheese, and then sprinkle evenly over the potatoes.

Bake in preheated oven at 180℃ (160℃ fan, Gas 4) for about 1 hour or until the potatoes and celeriac are tender and the top is golden brown.

Serve the gratin hot with a simple, mixed salad, and sprinkled with extra grated Parmesan cheese.