Preheat the oven to 350F. Line a baking sheet with parchment paper. Set aside.
Take the crust out of the fridge and place it on the counter.
Tape a large piece of parchment paper on the counter. unwrap the crust and place it on the parchment paper. Cover with another piece of parchment paper.
Using a rolling pin, roll out the crust to ⅛" thickness. Carefully transfer it to the baking sheet. It's ok if it's bigger than the baking sheet, we will fold the edges.
Fill the middle of the crust with the apple filling, don't use the juice that the apples have released by now. Leave two inches from the edges.
Gently start folding the edges inside to cover a little bit of the apples.
Whisk the egg and brush on the edges of the crust. Sprinkle wit granulated sugar.
Bake in the oven for 25-35 minutes until the crust is golden brown and the apples are baked.
Cool the galette on the counter for 15-20 minutes before slicing. Serve with vanilla ice cream if desired.