Preheat the oven to 350°F (180°C) and line a baking sheet with parchment paper. Set aside.
Peel, core and slice the apples ¼ inch (1½ cm) thick and place in a medium bowl.
To the bowl, stir in brown sugar, lemon juice, cornstarch and vanilla bean paste until well mixed, then gently fold in the blueberries. Set aside.
On a floured surface, roll out the pie crust on it into a ¼ inch (1 ½ cm) thick circle, and then transfer the crust to the prepared baking sheet. (If you wish, trim the edges of the pie crust to make a neater circle.)
Leaving a generous 2-inch (5 cm) border all around, pour the apple filling into the center of the pastry.
Fold the pastry edges up over the apples all around. The pastry will pleat slightly and the filling in the center will be exposed.
Whisk the egg yolk with the water to make an egg wash, and then brush over the pastry.
Sprinkle the pastry with granulated sugar and bake for roughly 45-55 minutes, or until the apples are tender and the crust is golden brown. If the crust starts to over brown before the apples are cooked, cover the pastry with a ring of tin foil.
Let cool for at least 30 minutes before serving with vanilla ice-cream. Store leftovers, loosely covered, at room temperature for up to 2 days.