• Cube the butter into 1-inch pieces and pop them in the freezer for 5 minutes to chill them.
• Mix the flour, sugar, and salt in a large bowl. Add the cold butter cubes to the flour mix and cut them into small pieces using a pastry cutter. Aim to keep large butter chunks and a few smaller ones. 
• Mix the lemon juice into the cold water. Slowly drizzle it into the flour mixture and mix it with a fork into a rough dough that sticks together when pressed. You want to achieve a cohesive dough that's not sticky, so adjust the water quantity as needed. If the dough gets warm or the butter melts, give it a chill in the fridge for about 10 minutes.
• Use a rolling pin to roll the dough into a rectangle on a floured kitchen counter. Then, fold the dough in thirds, like folding a letter. Rotate the folded dough, roll it out again, and fold. Continue this process until you've folded the dough six times. Optionally, you can trim the edges for more uniform layers as you fold.
• If you are making this on a cold day, then there is no need for any fridge rest between the rolling of the layers unless the butter is melting. In warm weather, the rough puff pastry will likely need a fridge rest between every second fold to ensure the butter stays chilled.
• After the last fold, form the dough into a round, wrap it tightly in plastic wrap, and place it in the fridge for at least 2 hours. It can also be frozen for up to 3 months.

Filling and assembling

• Peel and core the apples and slice them into equal ¼-inch slices.
• Mix sliced apples, brown sugar, lemon juice, zest, cornstarch, spices, salt, and vanilla in a large bowl. Stir to combine it all. Set aside.
• Remove the chilled pastry from the fridge and roll it into a 13-inch/ 33cm circle on a lightly floured surface. Transfer the circle onto a large piece of parchment paper.
• Arrange apple slices at the center of the puff pastry, leaving a 2-inch border around the edges of the puff pastry. Leave any apple liquid behind.
• Fold the puff pastry edge over the apples, creating a rustic look. Brush the puff pastry crust with the egg wash for a golden brown finish. Sprinkle the sides of the pastry with coarse sugar.
• Bake at 400°F/ 200°C for 15 minutes, then turn down the oven temperature to 350°F/ 180°C and bake for a further 45-50 minutes until the filling is bubbling and the pastry is deeply browned.
• Let the baked galette stand for around 20 minutes before slicing with a sharp knife. Optional- Brush the baked apples with 1 tablespoon of warmed apricot jam.
• Serve warm, preferably with a scoop of vanilla ice cream.