Makes 12–14

For the dough:

300g plain flour

2 teaspoons sugar

In ½ teaspoon salt

80ml oil (vegetable, sunflower or olive are all fine)

150ml water

1 teaspoon white wine vinegar

For the filling:

750g floury potatoes, peeled

1 large onion, finely chopped

100–120ml olive oil, plus extra for cooking and brushing the pastry

250g chestnut mushrooms, diced

Salt and black pepper, to taste

First, prepare the dough: mix the flour, sugar and salt in a large bowl. In a separate bowl or jug, whisk the oil, water and vinegar together, then add this to the dry ingredients. Stir to combine, then knead very briefly under the heel of your hand – just enough to create a smooth, slightly sticky dough. Place in a large bowl, cover with cling film and leave to rest for 1–2 hours. This resting period is important: it’s during this time that the flour will become fully hydrated and the dough will ‘relax’, making it easier to roll out. The vinegar helps with this, too, making the dough less taut and more supple.

While the dough rests, start making the filling. Cut any particularly large potatoes into halves or quarters, then place them in a large pan of cold water. Salt the water generously then place over a high heat. Once the water reaches the boil, reduce the heat slightly and cook the potatoes for 15–20 minutes, or until they’re tender enough to prick with a fork. Drain them and set aside to cool slightly

Over a low heat, cook the onion in a splash of oil with a pinch of salt for 20 minutes. The onion should be very soft and translucent. Add the diced mushrooms and cook for a further 10 minutes or so, leaving the onions and mushrooms softened.

Preheat the oven to 200°C/fan 180°C/gas mark 6 and brush a large baking tray with a little oil. Mash the cooked potatoes with the olive oil, to give a smooth but not sloppy mash. Stir in the mushroom and onion mixture then season very generously with salt and pepper. Generously flour the work surface, then roll out the rested dough until it’s very thin. It should be 60–70cm long and around 35cm wide. Keep flouring the surface and the rolling pin as you go to prevent sticking. Now brush all over the surface of the dough lightly with olive oil. Spread the filling in a 4–5cm-thick line along one of the long edges of the dough. Working quickly but gently, roll this log of filling up in the pastry to give a fat 60cm-long roll. Trim the ends, which are likely to be tapered and messy, then cut the roll into 12–14 slices, each around 5cm wide (see photographs here). For each slice, gently pinch the cut ends to bring the pastry together and seal the filling inside. These pinched ends will be the tops/bottoms of the pastries. Arrange them on the greased baking tray and press each down to a fatter, squat shape – each pastry should be shaped into a thick disc. Brush the pastries lightly with olive oil and bake for 30–35 minutes, until golden and crisp. Serve while they’re still hot