Cover the bottom and sides of a 9-inch springform pan with extra large aluminum foil so that the no water can leak in (it’s worth a trip to the store to buy the 18″ wide foil). Wrap it with two layer for extra security. Crimp the top of the foil around the top edge of the springform pan. You can also place the springform pan in a slightly larger cake pan (10″) that has 2″ sides (I ran out of big foil but had a nice cake pan that it just barely fit into. I didn’t have to worry at all about the foil keeping water out).
Preheat oven to 350 degrees, placing the top rack in lower third of oven.
In a large mixing bowl, mix together the finely ground cookie crumbs with the sugar and salt. Pour the melted butter over top and mix until the crumbs become coated.
Pour into the prepared springform pan and gently smooth out (I like to use a metal measuring cup for this). Carefully work the crumbs up the sides so that they are 1 1/2″ tall and approximately 1/4″ thick. You should have a nice layer on the bottom and the sides should go about halfway up your pan. Place into the oven and bake for 8-10 minutes or until lightly golden brown. Turn oven down to 325 degrees.
Beat the cream cheese, granulated sugar, and eggnog on medium-low speed for approximately 2 minutes or until smooth and creamy. With mixing speed on low, gradually add the sour cream, vanilla extract, cinnamon, and nutmeg. With mixing speed on low, add the eggs one at a time, mixing until incorporated, then beat on high for 1 minute.
Place the prepared springform pan into a large high-sided roasting pan. Pour the cream cheese filling into the springform pan, smoothing out the top with a spatula. Pour boiling water around the springform pan, taking care not to get any on the filling. You’ll want the water to go halfway up the side of the pan (this was just to the lip of my 2″ tall cake pan). Place in the oven and bake at 325 degrees for 1 hour and 45 minuets. If you like extra firm cheesecake, continue baking for an additional 14 minutes for a total of 2 hours.
After the cheesecake has baked, turn off the oven, slightly crack the door open and allow to cool for 1 hour. This is the key to getting a perfect top without it falling or cracks forming.
Remove the cheesecake from the bath and dry the bottom of the pan. Place in the refrigerator on a wire cooking rack to chill for at least 4 hours before serving, I prefer 6+ hours. Wrap the top of the cheesecake with foil after 30 minutes in the refrigerator (giving the cheesecake 30 minutes will help prevent condensation from forming on the underside of the foil).
Prepare the topping by beating the heavy cream, eggnog, vanilla, and powdered sugar with a handheld mixer or in the bowl of a stand mixer fitted with the whisk attachment, until stiff peaks form. Fold in mascarpone. Using a spatula, spread over the top of the cooled cheesecake (you can also do this at about 3 hours into the chill time so that it can set during that remaining hour). During the chilling process the cheesecake should come away from the edges of the pan, making it easy and mess-free to remove it before serving.
Slice and serve immediately. Dust with nutmeg, if desired.