Preheat the oven to 350°F. Prick the sweet potatoes in several places with a fork, and bake the sweet potatoes right on the rack for 1 1/2 hours, until very soft. Leave the oven on. Remove and cool the potatoes until they are just slightly warm, then peel the skins off, and puree in a food processor or blender, or pass them through a ricer, and place in a large bowl. You should have about 1 ¼ to 1 ½ cups puree.
Unroll the prepared pie crust and fit it into a 9-inch pie plate. Attractively crimp the edges of the crust. (Or if you've purchased a pre-made pie crust already in the pan, skip this step).
For the filling, in a large bowl, whisk together the eggs and orange zest. Whisk in the pureed sweet potatoes, and then add the sugar, cinnamon, ginger and salt and whisk into the sweet potato mixture until blended. Slowly whisk in the cream until well combined. Pour the filling into the prepared pie crust.
Bake the pie for about 1 hour, until the filling is set. You can test this by inserting a sharp knife near the center; when it come out clean, the pie is done. Cool the pie completely on a wire rack. The pie will be a bit puffed up when it comes out of the oven, then sink slightly as it cools. You can serve immediately, or cover and refrigerate for up to 2 days.