To make the pastry place the flour, butter, egg yolks and generous pinch of salt into a food processor and blitz until the mixture becomes crumb-like.
Slowly add the water until a ball of pastry appears - you may not need all the water.
Wrap the pastry in cling film and leave it to rest in the fridge for an hour.
To make the filling peel and chop the potato, onion and swede into 1cm dice and add to a medium sized bowl.
Cut the beef into similar sized chunks and add to the bowl.
Season generously, add the flour and then mix everything together well and set aside.
Preheat the oven to 180c.
When rested, divide the dough into 6 equal sized balls. Roll out each ball to approx 25cm in diameter, then use a dinner plate as a template to ensure each disk is uniform and neat.
Divide the filling between each pastry disk, piling up on one half of the circle and leaving a gap around the edge. Divide and dot over the butter then brush the beaten egg around the edges of each circle.
Fold each in half to encase the filling, then crimp the edges to seal, you can twist, pleat or use a fork. Brush with the remaining beaten egg then use a small sharp knife to make a steam hole in the centre.
Put the pasties on a greaseproof paper lined baking tray (you may need to use two) and bake for 45 minutes or until the pastry is golden and the filing is cooked through.