Divide the butter into 4 portions
Put the flour and salt into a bowl, stir briefly then add 1 portion of the butter (cubed) and rub in with your fingertips
Pour in ¾ of the water and mix, with a blunt knife, to a soft dough, adding more water as necessary (do not add so much that the dough turns sticky)
Roll the dough into a long rectangle on a lightly floured worktop to approx 4mm thick. Take another portion of the butter, cube it and scatter over ⅔ of the dough, leaving the final ⅓ empty
Fold the empty third of the dough over the top of the dough, bringing it to the centre. Fold the other end of the pastry over the top, then rotate the pastry 90 degrees
Repeat steps 4-5 twice more to incorporate the remaining 2 portions of butter
When all of the butter has been used, rotate the pastry and roll out once more, then fold it and repeat. Fold up again then wrap before chilling for 1 hour in the fridge
Meanwhile preheat the oven to 200C/ 400F/ GM 6
Remove from the fridge, roll out the pastry to 3mm thick and use a round cutter (about 8½cm) to cut out 12 bases and place them into muffin trays. Fill with mincemeat (around 2 teaspoons per pie)
Cut 12 lids using a smaller cutter to fit, brush the underside with beaten egg and place them on top of the mincemeat. Gently press the pastry lids to the side of the pies to seal them
Glaze with the beaten egg, sprinkle with demerara sugar (optional), make a small cut in the tops and bake for 10 minutes then turn the oven temperature down to 180C/ 350F/ GM 4 and bake for another 10 minutes
Let cool in the muffin tin