First make the pastry, place the flour and butter in a stand mixer with the beater attachment fitted. Gently mix until it resembles breadcrumbs.
Add the icing sugar and mixed spice and mix through, then add the egg yolk and the milk and mix until it starts to form a dough.
Take the dough and shape it into a block about 1cm thick, this will make it easier to roll out later. Rest in the fridge for at least 1 hour.
Take two 12 hole deep muffin tins and grease 18 cavities with a little butter. Roll out the pastry to a thickness of around 1/2 a cm and using a round cutter a bit larger than your muffin tin holes, cut out circles and fill each of the holes with pastry rounds.
Press the pastry into the sides so that it comes up the sides of the tin. Take care not to pierce the pastry, you'll need to keep rolling the scraps to get all 12 rounds. Place in the fridge to chill for around 30 mins.
To make the frangipane put the butter and caster sugar in the bowl of a stand mixer fitted with the paddle attachment and beat until smooth.
Add the eggs in batches and beat until combined. Then using a spoon or spatula, add the ground almonds, ground pistachios and flour, fold them in gently until smooth. If you have a piping bag, place the frangipane in the piping bag, ready to pipe it into the pastry cases. If you don't have a piping bag, a spoon will do.
Preheat the oven to 170C Fan/180 C/Gas 4. Take the chilled pastry cases from the fridge and place a heaped teaspoon of mincemeat in the base of each pastry case. Make sure you leave plenty of room for the frangipane.
Pipe a spiral of frangipane in the top of the pie, you want to cover all of the mincemeat so none can escape. Be careful not to fill them too much as the frangipane will rise, you want to come just to the top of the pastry edges.
Place the pies in the pre-heated oven and bake for 35-40mins or until golden, you want the pies to be golden on top and you want to be sure the pastry is cooked on the bottom. When done leave them in the tins to cool completely before removing.
These keep well in an airtight container for at least 3 days and they also freeze very well.