4 tablespoons (1/2 stick) unsalted butter (melted, plus butter for greasing the baking pan)
5 large ripe organic (pitted and sliced into 1/2-inch wedges, if the nectarines aren't organic, be sure to peel them first)
1 1/4 cups Sugar
1 tablespoon cornstarch
  finely grated zest of 1 lemon
1 tablespoon fresh lemon juice
1/4 cup minced crystallized ginger
1 cup unbleached all-purpose flour
1 teaspoon baking powder
1/4 teaspoon salt
1 large egg
3/4 cup sour cream
  Whipped Cream or vanilla ice cream (for servings, optional)