Classic Cornish pasties

Method

1. Freeze the margarine and lard 
for at least 1 hour until very firm.
2.  Sift the flour and salt into a large mixing bowl. Remove the margarine and lard from the freezer and coarsely grate them on a box grater straight into the flour, flicking some of the flour onto the fats as you work if they start to get a little sticky.
3. Rub the grated fats into the flour 
with your fingertips, then mix in the 
ice-cold water using a dinner knife until 
it all comes together into a soft dough.
4. Turn the pastry out onto a lightly floured surface and knead for about 1 minute until smooth and slightly elastic. Wrap in cling film and chill for 1 hour.
5. Meanwhile make the filling. Mix the steak, swede and potatoes in a bowl 
with the chopped onion, 1 tsp salt and 
½ tsp freshly ground black pepper.
6. Weigh the pastry, divide into 6 equal pieces, then roll out each piece on a lightly floured surface to a 20cm circle. Weigh the filling, divide equally into 6 and pile it into the centre of each circle. Use your hands to pack it gently into a rugby-ball shape that sits across the centre of each pastry circle. Brush one half of each pastry edge with a little water, then bring it over the filling and press the edges together well. Fold over and crimp the edge with your fingers to give a good seal. Put the pasties, spaced well apart, on a baking sheet 
lined with non-stick baking paper and 
chill for 1 hour.
7. Heat the oven to 180°C/160°C fan/gas 4. Remove the pasties from the fridge and brush them generously with the beaten egg. Make 3 small slits in the top of each pasty and bake for 1 hour until richly golden. Transfer the pasties to a wire cooling rack and eat while still warm.