Thaw the puff pastry sheets in the fridge overnight or at room temperature for a few of hours.
1 package puff pastry
Peel and slice the apples and toss them into a large bowl. Squeeze the juice of one large lemon on top of the apples and then add the sugar, cinnamon, nutmeg and vanilla.
10 medium-large apples, 1 large lemon, 1/2 cup (100g) light or dark brown sugar, 2 tsp cinnamon, 1/2 tsp nutmeg, 1 tsp vanilla
Toss all the ingredients together and then allow it to macerate for 1-2 hours.
On a lightly floured surface, roll out one of the puff pastry sheets an extra 1-2 inches on each side so that it hangs over the end of a deep dish pie plate.
Flour for dusting
Use a slotted spoon to remove the apples from their bowl and place them into another bowl, reserving the excess juice.* Toss the apples with the cornstarch and then place them over the bottom puff pastry sheet.
4 heaping Tbsp (40g) cornstarch
Repeat with the top puff pastry sheet and place it on top of the apples. Trim off any excess puff pastry and fold the ends of the sheets over one another so they’re sealed. Crimp with your finger along the edge of the plate and cut a few slits in the top of the crust.
Refrigerate the pie for 30 minutes and preheat the oven to 350F (177C) conventional (no fan).
Place the egg into a small bowl and use a fork or a small whisk to beat the egg vigorously until it’s runny. Use a pastry brush to egg wash the puff pastry pie crust and then top with raw sugar.
1 large egg, 1-2 Tbsp raw sugar
Bake for 75 minutes on the bottom rack of the oven. The juices should be bubbling through the slits of the crust. If they're not bubbling and the edges of the pie are getting too dark, feel free to cover them with the foil and bake for an additional 5-20 minutes.
The pie will set up nicely as it cools but if you serve it hot, it is more difficult to slice.