Place the prepared apples into a large mixing bowl. Add the sugar, cornstarch, cinnamon, and vanilla. Mix with a wooden spoon until the apples are fully coated.
Place the chilled pie dough onto a lightly floured work surface. Roll it out into a large circle, about 35cm (14 in.) in diameter.
Place the rolled out dough onto a square of parchment paper, and place either onto a large baking sheet or large round baking tin.
Top the pastry with the almond flour, leaving about 5cm (2 in.) from the edges free.
Arrange the apples in concentric circles over the pastry, leaving about 5cm (2 in.) exposed border of crust around the edges.
Fold the edges of the pastry over the apples, pressing gently at any points where the pastry folds over itself to ensure that it holds together.
Optionally brush the top of the pastry with egg wash and sprinkle with coarse sugar.
Bake for 35-40 minutes, or until the pastry is golden brown and the apple filling is bubbling.
Cool for at least 10 minutes before slicing and serving.