Preheat the oven to 190°C/374°F/gas mark 5. Line a baking sheet with baking paper
Add the diced potatoes to a saucepan and cover with cold tap water. Add salt to taste, as a guide, around 1/2 to 1 teaspoon.
300 grams potato
Place the saucepan over medium-high heat and bring the water to a rolling boil. A rolling boil has large bubbles continuously rising rapidly to the surface. It is more vigorous than a gentle simmer. Once boiling, cook the potatoes for only 2 minutes.
Drain the potatoes thoroughly in a colander and transfer them to a large bowl to cool down.
In a large frying pan over medium heat, melt the butter.
20 grams butter
Add the chopped onions and stir them through the melted butter.
200 grams onion
Place a lid on the pan and gently fry the onions over low heat for 6 minutes, stirring every minute. If using a gas stove with settings 0-9, fry around gas mark 3. The onions should be soft and translucent with some caramelised bits, not too browned. Transfer the onions into the bowl with the potatoes to cool.
Roll the puff pastry out on the work surface. A handy tip - you can keep the pastry on top of the paper it was rolled in to avoid flouring the counter. This saves cleaning up later. 1 sheet puff pastry
When unrolling the pastry, you may notice that the innermost part of the curl might have some cracks. Simply use your clean fingers to gently smooth over the cracks and seal any breaks in the pastry.
Roll the pastry sheet slightly larger, to about 40cm x 25cm. Ensure the pastry is not sticking to the paper before you carry on. If it is, flip the sheet over and pull the paper away. Replace the paper and flip it back over. To prepare the pastry, slice the sheet lengthwise in half, then cut each half into four equal rectangles. This will give you equal portions for your pasties.
Add the cheese, cream cheese and parsley to the cooled potato-onion mixture. Season to taste with salt and pepper.
190 grams mature cheddar cheese, 3 tablespoons cream cheese, 1 tablespoon fresh, chopped parsley, salt and pepper to taste
Gently stir everything together until fully incorporated with an even cream cheese distribution.
Scoop equal amounts of the pasty mixture onto four of the puff pastry rectangles.
With a pastry brush, generously brush the beaten egg around each mound of the filling, making sure to cover the edges where the pastry will be sealed. This will help create a secure seam when you fold and seal the pasties. 1 egg
Take the remaining pastry rectangles and place them on top of the filled ones. Press the edges of the top and bottom sheets together firmly to seal the pasties.
To seal the edges of the pastry, use a fork to crimp them shut. Be cautious not to press the fork's tines into the filled part of the pasty while doing this.
Brush the top of each pasty with the remaining beaten egg.
Optional - Sprinkle over sesame, poppy or nigella seeds and place the cheese and onion pasties on the lined baking sheet.
sesame seeds, poppy seeds or nigella seeds for sprinkling
Using the tip of a knife, gently stab two small steam holes in the top of each pasty. These holes will allow steam to escape during baking, preventing the pasties from becoming too soggy and ensuring a nice texture. Bake for 20-25 minutes, or until the pastry is puffed up and a light golden brown.