Preheat the oven to 350 degrees F.
Wrap the sweet potatoes tightly in 2 layers of aluminum foil and roast them in the oven until very soft, about 1 hour and 15 to 20 minutes. Remove from the oven and allow to cool.
In a bowl, stir the graham cracker crumbs and brown sugar until well combined. Add the butter and mix until the crumbs are evenly moistened. Press firmly and evenly on the bottom and sides of a 9-inch pie plate to create a crust, being sure there are no cracks. Bake in the oven for 10 minutes or until golden. Remove from the oven.
Meanwhile, make the filling: Unwrap the potatoes and peel them. Put the flesh into a bowl and mash well with a fork. Add the eggs, 1/2 cup brown sugar, cream, flour, cinnamon, nutmeg, and vanilla and whip until very smooth with a whisk. Pour the filling into the partially baked crust. Sprinkle about 1 tablespoon brown sugar over top and bake in the center of the oven until set, about 40 minutes.
Allow the pie to cool completely before cutting. Serve at room temperature.