Preheat the oven to 350 degrees F (175 degrees C).
Arrange peach slices in a 9-inch round baking dish. Pour about half the reserved peach juice on top; discard remaining juice. Beat egg, flour, and sugar in a bowl until combined; pour over peaches. Drizzle melted butter over the flour mixture.
Bake in the preheated oven until golden brown, about 45 minutes.
