Preheat oven to 350° F (175° C) if not still preheated.
In the bowl of a stand mixer, mix the cream cheese, sugar and cornstarch together with a paddle attachment for two minutes on medium speed until everything is smooth and there are no lumps. (You can alternatively use a hand mixer). Scrape down the sides and bottom of the bowl to ensure everything has been mixed well.
32 oz (907 g) cream cheese, softened, 1 1/4 cups (250 g) granulated white sugar, 1/4 cup (32 g) cornstarch
Add in the pumpkin puree, sour cream, pumpkin pie spice and vanilla. Mix for 1 minute on medium speed. Scrape sides and bottom of the bowl again.
1 cup (244 g) canned pumpkin puree, 1/3 cup (82 g) sour cream, at room temperature, 1 tbsp pumpkin pie spice, 1 tbsp vanilla extract
At this point, stop and put a pot of water on the stove to start boiling. You will want enough water to go about 1 ½ inches up the sides of the springform pan.
Next add in the eggs and egg yolks one at a time to the cheesecake batter. Mix on low speed, ensuring that each is fully mixed in before adding the next. As soon as the last one is fully mixed in, turn off the mixer. Do not over mix the batter.
3 whole eggs, at room temperature, 2 egg yolks, at room temperature
Pour the half the batter into the prepared pan with the crust, then use an offset spatula to smooth it out into an even layer. Sprinkle the spiced brown sugar over the batter in an even layer. Then pour the remaining cheesecake batter on top, smoothing it out with an offset spatula. Sprinkle the chilled streusel over the top. The pan will be full, but that is okay!
Place the cheesecake in a large roasting pan in the oven. Slowly pour the boiling water into the pan around the cheesecake being careful not to splash the cheesecake.(If you're using the 10-inch pan method, place the cheesecake in the 10-inch pan, then place the 10-inch pan in the large roasting pan. Pour water around the 10-inch pan.) Bake at 350° F (175° C) for 1 hour and 30 minutes. (If you see the streusel getting too browned towards the end of the 1.5 hours, loosely cover with aluminum foil.) When 1.5 hours are up, turn the oven off and crack the oven door open using a wooden utensil. Let the cheesecake stay in the oven for 1 more hour. The cheesecake will continue to bake as it is cooling. Once the 2 hours and 30 minutes are up, remove the cheesecake from the oven and carefully go around the edges of the pan with a butter knife to loosen the crust from the sides of the pan. Let the cheesecake cool completely on the counter, and then refrigerate until completely cold, 8 hours or overnight.