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.
Next make the apple filling as you want this nice and cold for when you use it. Place the apples, butter, sugar and mixed spice in a saucepan and cook over a low heat for about 15 minutes until softened and pulpy. Place in a bowl and leave to cool, then transfer to the fridge.
Finally make the streusel, mix the flour, sugar and salt in a bowl and then pour over the melted butter. Using a fork stir the mixture until it all clumps together. You need a mix of small crumbs and big chunks. Add the chopped pecans and stir them gently through the streusel. Put the streusel in the freezer for 10-15 mins to cool.
When ready to assemble, pre-heat the oven to 180C and take a 12 hole deep muffin tin and grease it 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.
Take care not to pierce the pastry, you'll need to keep rolling the scraps to get all 12 rounds. Using a fork prick a few holes in the base of the pastry.
Take the apple filling from the fridge and spoon it into the pastry holes, add a generous amount, but don't add too much so that it overflows. Take the streusel topping and sprinkle it over the apple filling.
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 can be stored in the fridge and eaten within 2 days, or you can freeze them and defrost them fully before eating. They are nice warmed in the oven and served with cream.