- 2 tbsp olive oil
Probably the most widely-used oil in cooking, olive oil is pressed from fresh olives. It's…
- 2 onions, thinly sliced
Onions are endlessly versatile and an essential ingredient in countless recipes. Native to Asia…
- 2 thyme sprigs, leaves picked, plus extra to serve
This popular herb grows in Europe, especially the Mediterranean, and is a member of the mint…
- 150ml double cream
- 175ml milk
One of the most widely used ingredients, milk is often referred to as a complete food. While cow…
- 1¼kg/2lb 12oz large potatoes, peeled and thinly sliced
The world's favourite root vegetable, the potato comes in innumerable varieties. A member of…
- butter, for greasing
Butter is made when lactic-acid producing bacteria are added to cream and churned to make an…
- 100g crème fraîche
- 85g Parmesan, grated
Parmesan is a straw-coloured hard cheese with a natural yellow rind and rich, fruity flavour. It…
Up to 2 days before serving, heat oven to 200C/180C fan/gas 6. Heat the oil in a large frying pan. Add the onions and thyme, cover, and cook over a gentle heat for 10-15 mins until softened and caramelised. Pour the cream and milk into a large bowl and season well. Add the potatoes and mix to combine.
Butter a 23 x 28cm ovenproof dish, then layer in half the potatoes. Spread the onion mixture on top, then layer on the remaining potatoes. Press down with your hands. Pour over the milk mixture, which should come just level with the potatoes. If not, add a little more milk until it does. Cover with foil, then bake for 11⁄2 hrs until tender. Remove from the oven and leave to cool. Cover and store in the fridge.
On the day, heat the oven to 220C/200C fan/gas 7. Uncover the gratin, spread the crème fraîche on top, then sprinkle over the Parmesan. Put in the oven and cook for 30 mins until the cheese is melted, the top crisp and golden brown, and the gratin piping hot. Serve garnished with extra thyme.