Use a fork or a knife to puncture several deep slits in the sweet potatoes. Place on a baking sheet and set on the middle rack of a cold oven. Set the temperature to 350 °F and roast the sweet potatoes until fork-tender, 90 to 120 minutes. Once soft, remove the sweet potatoes from the oven, slice them open, and scoop the flesh from inside the skin. Using a food processor or blender, puree the sweet potato flesh until completely smooth. Set aside to cool (this step can be done up to two days in advance; refrigerate the sweet potato puree once cooled.)

Combine the finely-crushed gingersnap crumbs and melted butter until thoroughly mixed. Press this mixture into a 9-inch springform pan across the bottom and extending 1 to 2-inches up the sides. Bake at 350 °F for 12 minutes, then set aside to cool. Reduce the oven temperature to 325 °F.

Using an electric mixer with the paddle attachment, beat together the cream cheese and both sugars until creamy and well combined, 2 to 3 minutes. Mix in the sour cream, 2 cups (565 grams) of mashed sweet potatoes, vanilla extract, cinnamon, ginger, nutmeg, and salt, stirring until well combined. Add the eggs, one at a time, mixing each in and scraping down the sides and along the bottom of the bowl. Do not over-mix the cheesecake - this makes it more likely to crack.

Wrap the springform pan in 3 layers of aluminum foil, or create a pan-in-pan water bath by placing the 9-inch springform pan inside a 10-inch cake pan (both pans together will be placed inside the water bath). Pour the cheesecake batter into the gingersnap cookie crust.

Place the springform pan or larger 10-inch cake pan inside a larger roasting pan and add hot water until the water level comes approximately halfway up the sides of the springform pan (or the outer cake pan). Bake at 325 °F for 75 minutes, or until the edges have set but a 3 to 4-inch diameter circle in the center of the cheesecake still jiggles. Turn off the oven and open the door slightly; cool in the warm oven for 30 minutes. After 30 minutes, remove the cheesecake from the oven and let it sit at room temperature for 1 hour before placing it in the refrigerator to chill for at least 4 hours, preferably overnight before unmolding from the springform pan.

If desired, top slices of the cheesecake with whipped cream and salted caramel sauce.