To make the pastry, weigh the margarine (hard from the refrigerator), then wrap it in a piece of foil and place it in the freezing compartment of the fridge for half an hour.
Meanwhile sift the flour and salt into a bowl, then when you take the margarine out of the freezer, hold it with the foil, dip it into the flour, then grate it on a coarse grater placed in the bowl over the flour. Carry on dipping the margarine down into the flour to make it easier to grate. When you have finished you will have a lump of grated margarine sitting in the middle of the flour.
Then take a palette knife and start to cut the fat into the flour (don't use your hands) until the mixture is crumbly. Now add enough water so that it forms a dough that leaves the bowl clean (you can use your hands for the dough), then place it in a polythene bag and chill it in the main part of the refrigerator for half an hour.
Meanwhile prepare the filling by first melting the butter in a small saucepan. Then take it off the heat and stir in all the filling ingredients quite thoroughly and leave it to cool.
Next turn the dough out on to a lightly floured surface. Roll it out to about 1/8 inch (3 mm) thick, then using a plain 3¼ inch (8 cm) cutter, cut the pastry into rounds. Put a teaspoon of the filling on to each round, then brush the edge of half the circle of pastry with water, and bring the other side up and seal it. Then bring the corners up to the centre, and pinch to seal well.
Now turn your sealed pastry parcel over, so that the seam is underneath, then gently roll the whole thing to flatten it to about ¼ inch thick (½ cm), and pat it into a round shape.
Place them all on a greased baking sheet and gash each cake diagonally across three times, using a sharp knife.
Now brush them with milk and sprinkle with caster sugar, and bake them in the oven pre-heated to gas mark 7, 425ºF (220ºC) for about 15 minutes until golden-brown.
Then transfer them to a wire rack to cool.