Preheat the oven to 180C/350F/Gas 4.
For the pastry, blend the flour, salt, and lard in a large mixer until the mixture resembles breadcrumbs.
With the motor still running, gradually add the water in a thin stream until the mixture comes together as a dough. If you don’t have a large enough mixer, rub the fat into the flour in a large bowl or clean bucket.
Wrap the pastry in cling film and chill in the fridge for 30 minutes.
For the filling, place the chopped chicken and flour in a large bowl and mix until the meat is coated in the flour. Season to taste with salt and freshly ground black pepper.
Season the vegetables with salt and freshly ground black pepper.
When the pastry has chilled, divide it into 40 pieces of equal weight. Roll out each piece of pastry onto a lightly floured work surface until it is just larger than the diameter of a dinner plate. Make sure you do not tear the pastry.
Using a dinner plate as a template, trim the edges of each piece of pastry to form a disc.
Spoon some of the chopped potato onto one half of each pastry disc, leaving 1.5cm/¾in free at the edges.
Spoon some of the chopped swede on top of the layer of potato, and then spoon some of the chopped onion on top of the layer of swede. Finally, spoon over some of the chicken.
Brush the edges of the pastry discs lightly all over with a little of the beaten egg.
Fold the empty half of the pastry disc over the filled half and either press the edges together with a fork, or twist the edges to seal.
Brush the top of each pasty with more beaten egg. Using a sharp knife, cut a small cross shape in the top of the pasties through which the steam can escape.
Place the pasties onto greased baking trays and transfer to the oven. Bake for 45-50 minutes, or until the pastry is crisp and golden-brown and the filling is cooked through and piping hot.
When the pasties are cooked, remove them from the oven and set aside to rest for 5-10 minutes before serving.