Remove dough from the fridge and slide the parchment paper off the cookie sheet and onto your worksurface.
Using a rolling pin, roll the dough (leave it on the parchment paper) into a 14-inch circle about 1/8 inch thick. Don't worry if the edges are a little ragged.
Slide the parchment paper with the dough back on the baking sheet (the pastry will curve up the lip of the pan a little bit).
Sprinkle 1 tablespoon flour evenly over the pastry, smoothing it out with your fingers.
Arrange the apple slices on the dough. Overlap slices in a circle, starting in the center and working your way out to about 3 inches from the edge.
Fold the edges of the dough up and over the apples in a free-form fashion. Fold dough towards the center, working all the way around, creating pleats as you go. Patch up any tears by pinching the dough together.
Use a pastry brush to brush the pleated dough evenly with beaten egg.
Sprinkle 1 tablespoon of the Demerara sugar over the top crust and 1 tablespoon over the apple slices.
Chill the tart in the fridge for 30 minutes.