Mix the flour with salt. Cut in the cold butter until the mixture becomes crumbly.

In a separate bowl, whisk together the egg, vinegar, and cold water.

Blend the wet ingredients into the dry mixture until it forms a dough. If needed, add a touch of cold water to bring the dough together. Wrap the dough in plastic wrap and chill for at least 30 minutes.

Slice the peaches into thin, even slices. Combine them in a bowl with sugar, cornstarch, and cinnamon. Toss the mixture until the peaches are evenly coated.

Preheat your oven to 425°F.

Divide the dough in half, or keep it whole for one large galette. Roll the dough into a rough circle on a floured surface.

Arrange the peach slices in a concentric pattern in the center of the dough, leaving enough space around the edges to fold over.

Brush the exposed crust with the beaten egg and sprinkle with sugar.

Bake the galette for about 30 minutes, or until the crust turns golden and the peaches are tender. Allow it to cool slightly before serving. Enjoy your delicious homemade peach galette!