Combine the flour and salt. Cut butter directly into the flour. Stir to combine.
In a separate bowl, whisk the egg, water, and vinegar.
Combine all the dough ingredients together. If the dough is too dry, add a little water just until it sticks. Wrap the dough in plastic wrap and keep it refrigerated for at least 30 minutes.
Pie Filling
Slice peaches into thin slices. Place them into a bowl and sprinkle them with sugar, corn starch, and cinnamon. Toss until well coated.
Assembling the Pie
Divide dough into two equal pieces or keep it in one piece for a large galette. Roll out each piece into a circular shape (it doesn't need to look perfect, just ensure there are no holes).
Arrange the peach slices in circles, starting from the middle of the dough. Be careful to leave enough space on the outer edges so you can fold them over to form the crust.
Whisk the eggs together. Brush the crust with the scrambled egg and sprinkle on the sugar.
Bake at 425°F for 20 minutes, or until golden brown. Enjoy!