In a large bowl combine flour, almond flour, sugar and salt. Cut butter cubes into the dry ingredients using a pastry cutter or a knife until the flour is crumbly with small bits of butter.
Drizzle water and vinegar over flour mixture and toss with a fork until dough just starts to come together. Turn out onto a lightly floured surface and work gently to bring everything together and the dough has smoothed out.
Roll dough into a ball and then flatten into an approximate 6" disk. Cover with plastic wrap and chill for at least one hour.
Peel and core apples and then cut them into thin slices. Drizzle slices with the lemon juice as you slice to prevent oxidization.
To the apples add the sugar, flour, cinnamon and nutmeg. Toss to combine.
In a small bowl whisk together egg and milk.
Preheat oven to 375°F.
On a lightly floured surface roll dough to an approximate 13" circle adding a sprinkle of flour to the top and bottom as you go to prevent it sticking.
Trim dough to a neat 12" circle by using a plate or pie plate as a guide (see note). Roll dough onto your rolling pin and transfer to a large parchment-lined baking tray.
Pile filling in the centre and spread out towards the edge leaving a 1 1/2" border of plain dough.
Fold the dough edge up and over the filling, crimping slightly as you go around. Sprinkle the apples with dots of butter. Brush the pastry with egg wash and sprinkle with coarse sugar if desired. Bake in preheated oven for 40 minutes until the pastry is golden and apples are tender.
Remove from oven and allow to cool for at least 10 minutes before slicing into wedges and serving with ice cream.
-The pastry does not have to be a perfect circle. If you'd like a nice rustic look you can leave it as you roll it as long as it is an approximate 12"-13" in diameter and 1/8" thick.
-If you like a neater look you can also arrange the apple slices in a concentric circle. I'm partial to piling the apples in as they fall.