Start by making the brioche. In the bowl of a free-standing mixer, combine the salt, sugar, yeast, 6 eggs, both flours and 85ml of tepid water. Using the dough-hook attachment, mix on a slow speed until all the ingredients are combined; this should take about 3 minutes.
Increase the mixer speed to just over halfway and mix until the dough comes away from the sides of the bowl. Turn off the mixer and leave the mixture to rest for 5 minutes.
Turn the mixer back on and slowly add the butter, a little nugget at a time, until all of it is incorporated. Add a little more flour if the dough feels too sticky – it should come away easily from the sides of the bowl.
Place the dough in a separate, lightly oiled bowl, cover with a tea towel and leave to prove at room temperature until doubled in size, about 40 minutes.
Once it’s proved, knock back the dough by folding it onto itself. Cover and place in the fridge for 4 hours.
Next, make your shortbread. Cream the butter, sugar and vanilla until smooth and fluffy. Mix in the flour, until it comes together into a dough.
Place between two sheets of greaseproof paper and roll it out to the thickness of a £1 coin. Using star-shaped cutters (or any shape you like), cut out 24 biscuits.
Chill on a lined baking tray in the fridge for at least 10 minutes, until ready to bake.
Preheat the oven to 160ºC/gas 2–3, then bake the shortbread for 10 to 12 minutes, or until golden. Sprinkle with caster sugar, then set aside.
To make your crème pâtissière, place the milk, cream and cinnamon into a pan over a medium heat. While that’s heating, whisk the eggs, sugar and cornflour in a bowl.
Once the cream mixture has almost come to a boil, take it off the heat. Slowly pour a third of it into the eggs, whisking constantly – this step will gently bring up the temperature of the eggs without scrambling them.
Pour the mixture back into the rest of the cream mixture and whisk well. Place the pan back over the heat and whisk the mixture constantly until it starts to boil – this will take about 2 to 3 minutes.
Pour into a clean bowl and place a sheet of clingfilm on the surface of your crème pat, to stop a skin from forming. Leave the bowl in the fridge until needed.
Once the brioche has chilled for 4 hours, divide into 40 to 50g balls, roughly the size of golf balls, and place on a baking tray lined with baking paper. Cover loosely with clingfilm and leave to prove again until doubled in size, about 25 minutes.
Preheat the oven to 180C/gas 4.
In a bowl, combine all of the crumble ingredients and rub together with your fingers until the mixture resembles breadcrumbs. Set aside.
With lightly floured hands, poke an indent in the centre of each ball, then lift each one and gently pull the sides away to make a doughnut shape, being careful not to knock out too much air.
Place the brioches on the baking sheet. Use two fingers to gently increase each indent into a crater 3 to 4cm wide.
Working quickly, place a teaspoonful of crème pâtissière into the centre, topped with a couple of teaspoons of mincemeat.
Beat the remaining eggs together, then glaze the outside of the pies with egg wash, and top generously with the crumble mixture.
Bake for 12 to 15 minutes, or until golden brown, then remove from the oven and leave to cool.
Press the shortbread shapes on top of your mince pies, and serve.