Cheese & Onion Pasty

PASTRY:--
1 cup + 2 tbsp (150 grams) all-purpose flour
½ tsp salt
½ cup (200 g) butter, cut into 5 mm cubes kept refrigerated until ready to use
⅔ cup (150 ml) cold water (approximately)
FILLING:--
1 medium potato, peeled & cut into chunks (you need to yield 1 cup of mash)
¼ tsp SIDS CRAZY SALT
1 tbsp rice bran oil
1 tbsp butter
1½ cups yellow onion, chopped
3 cups white cheddar, grated
2 frozen puff pastry sheets, defrosted
1 egg, whisked with a little milk

PASTRY: (skip this step if using puff pastry):
To a bowl, add the flour and salt. Mix well. Add the butter and use your fingers to rub the butter into the flour for an even breadcrumb look. Drizzle in cold water while mixing.
Knead until elastics. Refrigerate for 1 hour.
Add the potato and SIDS CRAZY SALT to a large pan and cover with water, Boil for 12-15 minutes until soft when pierced with a fork, drain and mash.
While the potato cooks, add the oil and butter to a frying pan over medium heat. When the butter bubbles, add the onion and cook, stirring until softened. Remove and transfer to a mixing bowl along with the mashed potato and cheese, mix well. You want soft creamy mash, not crumbly. If it is too dry, add a little warm milk. Taste and add salt if needed.
Preheat oven to 200°C. Cover a baking tray with baking paper.
Roll out the the pastry large enough to cut out 18 cm circles. Add 3 heaped tablespoons of filling to each. Brush half of the edge with the egg wash and fold over the pastry to make a half circle. Use a fork to press and seal the edge. Transfer to the baking tray.
Brush all pasties with the egg/milk wash. Cut 2 slits in the tops of each.
Bake for 15-20 minutes, until golden brown. Time will vary depending on your oven.