Prick the sweet potatoes all over with a fork and lay on a foil lined bake sheet. Bake for 1 hour, rotating halfway through cook time.
Remove from oven and set aside until cool enough to handle.
When cool, peel and dice. Toss into a food processor and pulse until smooth,adding 1 to 2 tbs of water as needed.
To make the gingersnap crust
Preheat the oven to 350 degrees F.
Pulse the gingersnap cookies in a food processor until fine crumbs.
Measure out 2 cups and set aside any additional crumbs for another time.
Pulse the 2 cups crumbs with the brown sugar and salt. Add the melted butter and pulse until the mixture is like wet sand.
Press the gingersnap mixture into a 9" tart pan or 9" springform pan. Press up the sides with your fingers or the bottom of a glass for a nice even layer.
Freeze for 8 to 10 minutes then bake in the preheated oven 6 to 8 minutes. Remove and let cool completely.
Preheat the oven to 375.
Whisk the evaporated milk, eggs, and maple syrup in a bowl.
In the bowl of your stand mixer fitted with the paddle attachment, beat the 2 cups sweet potatoes just to fluff a bit. Add the evaporated milk mixture and beat to combine on medium speed.
Stir together the brown sugar, cinnamon, ginger, and nutmeg in a bowl. Add to the sweet potato mixture and mix to combine. Scrape down the sides as needed. Add the butter and mix once again.
Pour the sweet potato mixture into the prepared crust and bake for 20 to 25 minutes (I did mine in a 9" springform pan and it took 40-45 minutes), until a toothpick inserted in the center comes out clean. Allow to cool on a wire rack completely before making the meringue.
To make the meringue
Using a double boiler, or the metal bowl of your stand mixer, whisk the egg whites until frothy. Add the sugar and mix to combine.
Set the bowl over a simmering saucepan of water and cook for 6 to 8 minutes, until the sugar is dissolved, whisking constantly. Remove from the double boiler and set in your stand mixer.
Whisk the egg whites on high speed until stiff peaks form, about 3 minutes. Add the cream of tartar, whisk another 6 minutes, when the mixture holds those peaks, and add the vanilla. Whisk to combine. Seriously, we're going for stiff peaks here people!
Spoon the meringue over the sweet potato pie and swirl or peak with a spoon (my dad's a peaker, I'm a swirler). Brown with a kitchen torch. Slice and serve.