To prepare the pie:

1. Whiz the flour, sugar, and salt in a food processor to combine. Pulse in the shortening and butter, just until evenly dispersed in pea-sized clumps. Begin adding ice water 2 tablespoons at a time until moist clumps begin to form. Remove dough from food processor, form it into a flat round disk, and wrap in plastic wrap. Chill in the fridge for at least an hour prior to use.
2. When you’re ready to bake the pie, roll the dough out on a well-floured surface into a 1/8-1/4” circle about an inch larger than your pie plate on all sides. Roll the dough loosely back onto the rolling pin and lift it into the pie dish. Gently fit the dough into the pie plate and trim off any excess dough leaving a 1” border around the edge of the dish. Fold the lip of the dough under so that it extends just over the edge of the pie plate and crimp the edges as you prefer. Prick a few holes in the bottom of the dough with a fork and place the whole pan into the freezer to chill briefly, about 15 minutes. In the meantime, preheat the oven to 350 degrees.
3. In a large bowl, whisk together the sweet potato puree and evaporated milk. Add the egg and sugar, stirring just until combined. Add the remaining ingredients and stir to combine. Set aside while you bake the pie crust.
4. When the oven is preheated, remove the pie plate from the freezer and line the insides of it with a piece of parchment paper. Use either pie weights or dry beans/rice to weigh down the dough and bake for about 15 minutes. After this initial bake, remove the pie weights, brush the entire crust with a thin layer of egg wash, and bake for an additional 5 minutes. Remove the pie from the oven, pour in the filling, and bake for another 35-40 minutes or until the center of the pie is set and no longer really jiggly. About 10 minutes into the bake, gently cover the crust with a ring of foil to prevent the edges from burning.

To prepare the meringue:

1. Combine the egg whites, sugar, cream of tartar, and salt in a large bowl set over a pot filled with about an inch of simmering water. I use my stand mixer bowl set over a small saucepan, just make sure the bowl is not touching the water. Stir the mixture with a spatula until the brown sugar has dissolved. Remove the bowl from the heat and place on the stand mixer, adding the vanilla and cinnamon. Beat on medium speed with the whisk attachment until it becomes fluffy, and the continue beating an additional few minutes until glossy stiff peaks form. The bowl of the stand mixer should also be cool to touch. Spread the mixture on the cooled pie and use a torch to toast the top of the meringue. Alternatively, you can bake the meringue at 375 for about 10-12 minutes until golden.