Put the potatoes and the onion in a large saucepan.
Cover with cold water and 1 1/2 tsp of salt.
Bring to a boil then reduce to a simmer until the potatoes are starting to becoome just tender. Do not overcook.
Drain the potatoes in a colaner and set aside.
Open the can of corned beef and rough chop it.
Add the potatoes, onion and chopped corned beef to the empty saucepan with a 1/4 teaspoon of black pepper. With a fork or masher, break the mixture down to a chunky mixxture.
Test for seasonings.
remove to a large bowl, cover and set aside to cool. Once cool, refrigerate until completely cool.
To Asemble the Pasties
Line the baking sheets with parchment paper and preheat the oven to 350ºF.
Remove the dough from the refrigerator and allow to warm little on the counter to make it easier to work with.
Divide the dough into 8 equal pieces. Roll the each piece into a ball.
On a floured surface roll out each ball into a circle about 20 cm in diameter. Use a plate or saucer to cut around.
Place 1/8th of the filling on the pastry to one side leaving a 3/4" border all around. Brush the edge with beaten egg then bring the other side of the disc over the filling. Seal the edge either by crimping in traditional style or with a fork.
Transfer to the baking sheet and repeat with the remaining discs.
At this point you can either proceed to bake or refrigerate /freeze for later.
Brush the pasties with beaten egg. Make one or two slits in the toop of the pastry to allow steam to escape. Bake for 20 minutes.
Take the tras from the oven and brush again with beaten egg. Return to the oven for a further 5 - 8 minutes until the pastry is a nice golden brown.
Remove the trays from the oven and allow to cool for a few minutes before moving them..