In a food processor pulse together the flour, salt, and sugar until combined. Add the cold cubed butter to the food processor, and pulse 10 times until the butter starts to look like small clumps.
Pour in the ice-cold water one tablespoon at a time, and pulse until the dough starts to come together to form a ball. If it is still not forming into a ball after 4 tbsps add an additional tbsp.
Place the dough on a lightly floured work surface and form into a disk of around 4 inches. Doesn't have to be perfect! Then wrap it in plastic wrap and chill in the fridge for at least 30 minutes but up to two days.
Preheat your oven to 375 F.
Take your dough out of the fridge and plastic wrap, and onto a lightly floured surface. Roll your dough out to a 12-inch circle. Place the dough on a sheet of parchment paper and transfer it to a baking sheet.
Peel and core apples. Cut your apples into thin slices. Arrange them starting from the outside in whatever fashion you like. Be sure to leave around 3 inches of the border.
In a bowl combine the cinnamon and sugar and sprinkle the mixture over the apples. Also, place small pieces of cubed butter over the apples.
Lift the edge of the dough over the apples, folding it as you go around.
Mix an egg with 1 tbsp of water to form an egg wash and brush over the edges of the dough ( the outer crust).
Bake for 30 - 35 minutes, until the crust is golden brown. Serve with ice cream of your choice or whipped cream!
Notes
Be sure to use cold butter through-out the recipe. It will give you the flakey texture you need for the crust!