1. Preheat oven to 375 degrees. Combine peaches, cornstarch, lemon juice, and 3/4 teaspoon salt in a large bowl. Mix together brown sugar and vanilla seeds; stir into peach mixture, and pour into a 2-quart, 11-inch quiche dish or shallow baking dish. Dot top with butter.

2. Roll out dough to 1/8-inch thickness on a lightly floured surface. Drape dough over fruit, and trim edges to 1 inch. fold under dough, and tuck into dish to form a crust. Cut five 3-inch vents into the top. Brush top with egg, and sprinkle with sanding sugar.

3. Bake until juices are bubbling through vents and top is golden brown, about 1 hour. Let cool on a wire rack for at least 1 hour before serving.