Roll the dough out on a lightly floured surface to a 12-inch circle. Carefully transfer the dough to a 9-inch deep pie pan and ease the pastry into the bottom and sides of the pan. Press the dough into the shell and crimp the edges in a decorative pattern. Using the tines of a fork, lightly dock the base of the shell. Place the shell into the oven and bake until lightly browned, 12 to 15 minutes. Remove from the oven and brush the bottom with the egg white. Set aside until ready to use.
Rub the sweet potatoes with the vegetable oil and roast in the oven for 45 to 60 minutes, until very tender. Remove and set aside to cool. Peel the potatoes and pass the flesh through a fine mesh sieve using a rubber spatula. You should have about 1 1/2 cups of smooth sweet potato puree.
In a medium mixing bowl, combine the sweet potato puree with the sugar, maple syrup, ginger, cinnamon, nutmeg, cloves and salt. Whisk to combine. In a separate bowl, combine the heavy cream with the eggs and whisk to combine. Add the cream and egg mixture to the sweet potato mixture and stir to blend. Pour the batter into the prepared pie shell and place the pie on a sheet pan. Bake until the center is set and the tart is golden brown, 35 to 45 minutes. Remove the tart from the oven and allow to cool for at least 20 minutes before serving.
Basic Sweet Pie Crust:
Yield:1 pie shell
Sift the flour, sugar and salt into a large bowl. Add the butter and shortening. Rub the fats between your fingertips and thumbs, or use a pastry blender, until the mixture resembles coarse crumbs. 1 tablespoon at a time, work in enough ice water just until the dough comes together, being careful not to overmix.
Shape into a smooth ball of dough, flatten into a disk, and wrap in plastic wrap. Refrigerate for at least 30 minutes, and up to 2 days.