Preheat the oven to 180 degrees Celsius or 356 degrees Fahrenheit, and grease your cupcake tray liberally with butter.
Liberally (tapioca) flour a large piece of baking paper on a dry, clean bench.
Place the dough on the sheet and liberally flour the top. Cut off about 1/4 of the pastry to set aside for the tops of the pies.
Roll the remaining pastry out into a large rough rectangle, about 1/2 centimetre thick. If the pastry keeps cracking, allow it to warm up a little. If it’s too soft to handle, pop it in the fridge for 5 minutes.
Use a circular cutter significantly larger than your cupcake tray holes to cut the bases for the mince pies. Lower each pastry round into a cupcake tray hole, gently pressing it flush against the sides but without stretching the dough. Any tears can easily be patched up with your fingers, and excessive dough around the edges can be neatly trimmed.
Continue this process until you have lined 12 cupcake holes.
Stir the tapioca flour into the fruit mince until it’s well combined. This will thicken it a little and ensure it doesn’t seep out and create soggy pastry.
Fill the pastry with the fruit mince and place in the fridge while you make the lids.
Roll the reserved pastry out into a 1/4-1/2 centimetre rectangle, flouring liberally whenever necessary. Use a cutter the same size or a little bigger than the muffin tin holes to cut out circles or stars for pastry lids. Continue until you have 12.
Preheat the oven to 180 degrees Celsius and remove the pie bottoms from the fridge. Use the egg to lightly egg wash the sides of the pies, and then press the lids gently but firmly atop to secure. Paint the tops of the pies with the egg wash, and then sprinkle over the sugar, if you’re using it.
Place the minced pies in the oven for 20 minutes, or until they smell fragrant and have coloured lightly. Turn the grill function on and continue to cook the pies for another couple of minutes, watching closely. Remove them when they are golden brown on top.
The pies can be served warm or cold, and keep well in an airtight container for up to a week.