Place flour in a small bowl. Using a grater, quickly grate chilled butter onto the flour.
Quickly rub the butter with flour and obtain a breadcrumb-like mixture.
Add sugar, salt and orange zest into the butter mixture. Using a spatula mix everything together. You may need to break the orange zest up a bit. Add cold milk and give it a stir with a spatula to spread the milk out and create larger clumps of dough.
Using your hands quickly knead out a dough. This process should take no more than 10 seconds. Gather all the dough in one place, give it a circular shape and wrap it in a plastic wrap. Place the dough in the refrigerator for 30 minutes or until apples are ready to assemble.
Peel apples, cut them in half and remove the inner core from each half. Place the apple halves flat side down and slice them lengthwise at about 1/8 inch thick. Set aside until needed.
Take out chilled butter from the refrigerator and cut it in small cubes. Set aside until needed.
Take out the dough from the refrigerator. Use a piece of parchment paper to roll out the dough. It will be much easier to transfer the parchment paper onto a baking sheet. Roll the dough evenly into a thin circle (about 1/8 inch or slightly less). The diameter of the dough should be about 12 inches. Lift the dough gently in between rolls to make sure that it is not sticking too much. The dough shouldn’t be too thin and shouldn’t be too thick. Too thin of dough will rip. Too thick one will become cakeier. Neither of which we prefer. If the edges of the dough crack, gently pinch that side onto itself to remedy the situation. Some cracks are totally fine.
Leaving a 3-inch border on the dough, stack apple slices, one slice overlapping the other. I’d like to actually crowd the apple slices and not to leave much room in between them. Once the slices shrink during the baking process, the galette will look very rare and empty. Have the apple slices lay on each other with only quarter inch visible from the previous slice.
Once apples are stacked, turn the 3-inch empty edges of the dough onto the apples all around. Work gently and try not to rip the dough. The edges should lay flat, but they do not have to be super neat.
Randomly place butter cubes which we previously prepped on top of the apples. Sprinkle the sugar all over the apples (and butter).
Prepare the egg wash by simply fork-whisking the egg in a small bowl. Brush the sides of the galette with an egg wash and sprinkle the sides with a little brown sugar. Transfer the parchment paper onto a baking sheet and bake the galette at 400F until the crust turns golden brown.
This last step could be very optional. However, for me it is essential. I keep a bottle of apricot syrup in the refrigerator just for this purpose. This time I had one we buy from our local Colorado orchard. I’ve also heard so many great things on Wabry brand of apricot syrup. Whichever you can find, will work. Once the galette has baked through, while it is still hot, I paint the entire galette (including the apple part) with a little bit of apricot syrup.