In a food processor, pulse the flour and salt to mix.
Add the butter, cut into 1/4-inch tabs.
Pulse until the mixture forms into pea-sized clusters.
Add the water and pulse until the dough starts to come together. If crumbly, add one tablespoon of water at a time, pulsing between additions, until the dough starts to come together.
Roll the dough into a ball, then flatten into a disk.
Wrap in plastic wrap and refrigerate for at least an hour.
While the dough is chilling, combine the lemon zest and juice in a measuring cup.
Then slice one apple, with the skin on. A mandoline slicer can make this process easier.
Add 1/3 of the juice and zest mixture to the apple slices and toss well to prevent the apples from oxidizing and turning brown.
Continue until all apples as sliced.
Preheat the oven to 450° F and place a cookie sheet or tin foil in the rack below the center rack.
Remove the dough from the refrigerator and roll it to between 1/8 and 1/4 inch in thickness between two sheets of parchment paper.
Remove the top sheet of parchment paper.
Brush 1/4 cup of the apricot preserves to 1 inch of the edge of the crust.
Drain any excess lemon juice from the apples, then add the sugar 1/3 at a time, tossing well between additions.
Starting in the center of the crust, layer the apple slices in an overlapping concentric circle up to the 1 inch edge.
Use the parchment paper as a guide to fold the 1-inch lip of the crust over the apples a section at a time, creasing the crust after each section.
Pinch closed any cracks in the dough.
Brush the dough with the beaten egg.
Sprinkle the turbinado sugar over the apples and the crust.
Slide the galette with the parchment paper onto a pizza stone and place on the center rack of the oven.
Bake for 20 minutes, then turn the oven to 375° F and bake for 25-30 minutes more or until the crust is a dark golden brown.
Let stand for 10.
Meanwhile, in a small pan, heat 1 tablespoon of the apricot preserves with the water until a syrup is formed.
Before serving, brush the syrup over the apples until they are glossy and moistened. You will not likely use all the syrup or the galette will be too soggy.
Serve warm or at room temperature.