Preheat the oven to 375°. In a small bowl, mix the first 5 ingredients. In a large bowl, whisk the eggs. Whisk in the pumpkin, evaporated milk, and the sugar-and-spice mixture; pour into the piecrust. Bake until just set in the center, about 1 hour. During the last 10 minutes of baking, top the pie with toasted pepitas and chopped crystallized ginger, making a 2-inch border around the pie. Let cool completely on a wire rack. Serve with whipped cream, if using.