Combine the flour, salt, sugar, and yeast in the bowl of your stand mixer and mix to combine.
Add the milk and eggs and mix on low speed for 8-10 minutes. The dough will start to pull away from the sides of the bowl and have medium gluten development.
On medium speed, add the butter in, one tablespoon at a time. Wait until each piece of butter has been incorporated into the dough before adding the next. Mix at high speed until the dough is extremely shiny and strong and passes the windowpane test.
Transfer the dough to an oiled bowl and cover with cling film. Leave to proof to an hour.
While the dough is proofing, add the nuts to a dry frying pan and toast over low-medium heat. Toast until the nuts are fragrant and then place in a bowl. Add the mincemeat to the nuts and set aside until ready to use.
Return the dough to the bowl of the stand mixer and on low speed, add the fruit and nut mixture to the dough. Knead using the dough hook attachment until the mixture has been fully incorporated into the dough.
Transfer the dough back to an oiled bowl and cover with cling film. Leave to proof in a warm area for 60 minutes.
While the dough is proofing, prepare the almond paste. If the almond paste is already ready, divide into four equal piece and roll out into a log just under 1-¼" in diameter and 10" long. Wrap each log of almond paste in cling film and place in the fridge until ready to use.
Turn out the dough onto a lightly floured work surface and punch the dough down. Divide the dough into four equal pieces and shape into a rectangle.
Unwrap the almond paste log. If the log is longer than the rectangle of dough, press the log down so that it is the same length as the rectangle of dough. Place the log in the middle of a rectangle of dough. Fold dough over to seal in almond paste log. Place dough seam side down on a baking tray and proof for another 2 hours.