Preheat oven to 350°F / 175°C. Line the bottom and the sides of a 9-inch (23cm) springform pan with parchment paper. Set aside.
Crust: In a large bowl stir together graham cracker crumbs, sugar, and melted butter until combined and evenly moistened. Transfer to the prepared pan and press crumbs into the bottom and halfway up the sides with the back of a measuring cup. Freeze until filling is done.
Filling: In a large mixing bowl, using a handheld or stand mixer fitted with a whisk or paddle attachment, beat the cream cheese, sugar, and flour just until combined, smooth and no lumps remain. Add sweet potato puree*, cinnamon, nutmeg, and vanilla** and mix to combine. Add one egg at the time and mix just until combined before you add the next egg. Scrape down the bowl and add heavy whipping cream and mix until creamy. Don't overmix. Too much air in the filling can cause cracks while baking.
Pour filling into the crust and spread evenly. Place a piece of parchment paper underneath the springform pan and bake for 55-65 minutes until the edges look puffed and the top is set with a lightly wobble underneath. It still should wobble like pudding. Don't overbake. I baked mine for 60 minutes.
Turn off the oven, crack open the door, and let the cheesecake in the oven for another hour. Then remove from the oven and let cool to room temperature. Refrigerate at least 3 hours or overnight.
Meringue: Fill a saucepan 2 inches high with water and bring to a simmer over medium-low heat. Place egg whites, sugar, and cream of tartar in a heatproof bowl (preferably glass) and set over the saucepan. The bowl should not touch the water. Whisk continuously for 3-5 minutes until sugar is completely dissolved. (Make sure the meringue doesn't get too hot, or the egg whites will cook through, and the meringue won't be stiff but lumpy. Remove from saucepan in-between to cool down a bit, if necessary.) The meringue should be warm to the touch. Remove from heat and beat with an electric mixer fitted with a whisk attachment on high speed until shiny, glossy, and stiff peaks form, for about 5-7 minutes.
Pipe or spread meringue on top of the cheesecake. Store leftovers in an airtight container in the fridge up to 3 days.