Begin by preheating your oven to 200°C/400°F/Gas Mark 6.
Put the diced potatoes into a saucepan with water, bring to a boil and cook until they soften, usually taking about 10 minutes.
As the potatoes are boiling, melt the butter on low heat completely then add the onions with the salt and cook on low heat for 5 minutes until caramelised
Drain the potatoes then mash before adding into the onions, along with the rest of the ingredients
Mix everything together and then set aside to cool for at least 30 minutes
Take the puff pastry sheet and unroll it. Proceed to cut it into 4 rectangles.
On one half of each rectangle, spoon the cheese and potato mixture, making sure to leave some space around the edges.
Brush the edges with some beaten egg, then fold the other half of the pastry over the filling, ensuring that the edges are sealed by pressing them together with a fork.
Line a baking tray with parchment paper and place the pasties on it.
Brush the pasties with the remaining beaten egg.
Put the pasties into the preheated oven and bake for 25-30 minutes, or until they become golden brown and crispy.
Once they’re ready, take the pasties out of the oven and let them cool for a few minutes before serving.
