Root vegetable recipes: Gratin of parsnip, potato and wild mushrooms

By Diana Henry Published: 9:55AM GMT 19 Feb 2010

Serves four as a main course, six as a side

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500g (1lb 2oz) potatoes

500g (1lb 2oz) parsnips

425ml (15fl oz) double cream

140ml (4fl oz) sour cream

85ml (3fl oz) full-fat milk

2 cloves garlic,

very finely sliced

leaves from 2 sprigs thyme

200g (7oz) wild or cultivated mushrooms, or a mixture

15g (oz) butter

Peel the potatoes and parsnips and slice very finely a mandolin is best. In a large saucepan mix the two creams and the milk and bring the liquid to just under the boil. Add the sliced vegetables, garlic and thyme and cook gently for five minutes.

Cut up any mushrooms that are particularly big (I often use oyster mushrooms here and they just need to be halved). Melt the butter in a frying-pan, add the mushrooms and saut briskly over a medium to high heat. You want to get a good colour on them and also drive off the moisture, otherwise they will make your gratin watery.

Season the potato mixture really well and spoon half into a buttered gratin dish I use an oval one measuring 23 x 35cm (9 x 14in), 5cm (2in) deep. Spoon on the mushrooms then add a final layer of potatoes. Bake in an oven preheated to 180°C/350°F/gas mark 4 for an hour or until completely tender. You may need to cover the top with foil after 45 minutes to stop it becoming too dark.