This apple Galette is simple to put together and is so delicious!
Thaw the puff pastry according to the package instructions.
Preheat the oven to 400F.
In a medium bowl combine the apples, brown sugar, flour, cinnamon, salt and lemon juice and stir to combine.
Roll out the pastry (if it's not already rolled out) on a large sheet of parchment paper to around a 12" square (it doesn't have to be perfect). Transfer the pastry to the baking sheet and pile the apple mixture in the centre of the pastry, add the cold butter on top of the apples and fold up the sides of the pastry to half cover the apples, folding it slightly over each layer.
Using a pastry brush, lightly brush the pastry with the beaten egg (you won't use all of it) and sprinkle the pastry with the sugar. Bake until golden brown, around 30 minutes and serve with ice cream if desired.