Heat oven to 400° F. On a lightly floured surface, roll the pie dough into one 9-inch circle. Transfer to a parchment-lined baking sheet.
In a large bowl, toss the peach slices, cornstarch, lemon juice, ginger and 3 tablespoons sugar. Pour filling onto the pie crust, leaving a 2-inch border. Fold the edges of the crust over the fruit mixture.
Brush the milk or heavy cream on the crust and sprinkle with the remaining teaspoon of sugar. Bake until the crust is golden brown and the fruit is tender, 25 to 30 minutes.