Potato gratin

Method

1. Preheat the oven to 170°C/fan150°C/gas 3. Dice the potatoes into 2cm cubes and mix with the onion, flour, cheeses and parsley. Season well, then tip into a large ovenproof dish (about 30cm x 24cm x 5.5cm deep). Pour over the double cream.
2. Bake for 1 hour 45 minutes until it’s bubbling and golden and the potatoes are cooked. If it browns too quickly, cover the dish loosely wit