Step 1

Bring a saucepan of water to the boil and add the potatoes. Cover and cook on a simmering boil for about 15 minutes, or until the potatoes are tender. Mash the potatoes with the butter and milk and season to taste with salt and pepper. Leave the potato to completely cool.

Step 2

Preheat the oven to 200C/180C Fan/Gas 6. Lightly grease a baking tray with the butter.

Step 3

Place the mashed potato, cheese, mustard and spring onions in a mixing bowl. Stir to thoroughly combine. Season with salt and pepper to taste.

Step 4

Unwrap and place the sheet of pastry on a work surface. Cut the sheet into six even-sized rectangles. With a short side nearest you, place a third of the potato mixture on the lower half of each rectangle. Brush the edges of each rectangle with some of the beaten egg and fold over the top half of each rectangle to make a square pasty.

Step 5

Crimp the edges of the pasties with a fork and brush the tops with the remaining egg.

Step 6

Place the pasties on the prepared baking tray and bake for 20 minutes, or until golden-brown and risen. Leave to cool slightly on a wire rack and then serve while still warm.