Put your flour, salt, and sugar in your first medium-sized bowl.
Cut your butter into 1 cm-sized cubes and add it to your bowl with the dry ingredients. Mix this lightly with a mixing spoon.
In a second medium-sized bowl, add your egg, vinegar, and cold water and mix with a whisk.
Take the wet mix of eggs, vinegar, and cold water in the second bowl and pour it into your mixing bowl with your dry ingredients.
Take your hands and mix the dough together. Ultimately, begin to knead the dough with your hands until you can see that the dough is well incorporated. (See notes)
Cover the bowl with plastic wrap and place it in the fridge to cool for 6-24 hours.
Preheat your oven to 375 degrees Fahrenheit, and remove your dough to sit on the counter while the oven is preheating.
In a bowl, add slice and your sliced peaches, brown sugar, cornstarch, salt, and lemon juice. Then mix.
Roll out your dough to about 12-14 inches in width creating a circle.
Move your dough to a baking sheet covered in parchment paper.
Add peach mix to the center of the dough and move them around to create a beautiful center as desired. Make sure to leave about 2 inches of dough on the edges untouched by the peach mix.
Tuck the dough on the edges in section by section.
Take your egg and mix it with your brush in a small bowl, then brush it onto the edges of the galette. Then sprinkle some sugar all over.
Bake for 31-33 minutes. Allow it to cool on the baking pan for at least 10 minutes before moving. Enjoy!
