Cheese & onion empanadas

For the pastry, put the flour and salt in a large bowl. Rub in the butter with your fingertips until it resembles breadcrumbs (alternatively, pulse the flour, salt and butter in a food processor). Gradually add up to 75ml cold water, mixing with a cutlery knife (or pulsing again in the food processor), then use your hands to bring together into a dough. Shape into a flat disc, wrap in a food bag or baking parchment and chill for at least 30 minutes.

Meanwhile, put the oil in a large frying pan over a low-medium heat and add the onions with a pinch of salt. Gently sauté for 22-25 minutes until soft and golden. Remove from the heat and stir in the grated cheese until mostly melted, then set aside to cool.

Cut the pastry in half and put one piece on a lightly floured work surface. Thinly roll out to about 0.2cm thick. Use a small bowl (12-14cm diameter) to cut out circles – you should get about 5 – rerolling as necessary. Layer on a plate with baking parchment between the circles. Repeat with the remaining dough.

Preheat the oven to 180°C, gas mark 4, and grease 1 or 2 large baking tray(s) with oil. To assemble, cut the mozzarella into 10 chunks, then divide between the pastry circles, putting onto one side of each circle. Heap the onion mixture on top, then dip your finger into a small bowl of cold water and use to dampen the edge of half the disc. Fold the pastry over the top and seal in a half-circle, ensuring there are no pockets of air. Use your fingers to crimp and twist the edge, pressing down firmly to seal. Repeat for each circle, then put the empanadas onto the greased tray(s). Chill for at least 30 minutes.

Brush the tops of the empanadas with the beaten egg and sprinkle over the sugar, if using. Bake for 30-35 minutes until deep golden. Leave to stand for a few minutes before serving.