Preheat the oven to 350 degrees if not still preheated from the crust.
In a stand mixer, mix the softened cream cheese, corn starch and granulated sugar together with a paddle attachment for two minutes 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. This is a crucial step, if the cream cheese is not smooth here, the cheesecake will have lumps of cream cheese in it when it bakes, so really be sure to mix the cream cheese well.
32 oz. (907 g) cream cheese, at room temperature, ¾ cup (150 g) granulated white sugar, 2 tablespoon (16 g) corn starch
Add the Biscoff cookie butter, vanilla and sour cream to the cream cheese mixture. Mix for 1 minute. Scrape the sides and bottom of bowl again to ensure everything is mixed together.
1 cup (240 g) Biscoff cookie butter, 1 tablespoon (15 ml) vanilla extract, ⅓ cup (82 g) sour cream, at room temperature
At this point, stop and put a pot of water on the stove to start boiling for the water bath. You will want enough water to go up about 1 ½ inches on the sides of the springform pan.
Next add in the eggs and egg yolks one at a time to the cheesecake batter, 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 eggs, at room temperature, 3 egg yolks, at room temperature
Pour the batter into the prepared pan with the crust. Place the cheesecake in a large roasting pan in the oven. Slowly pour the boiling water into the roasting pan around the cheesecake being careful not to splash the cheesecake.
Bake at 350 degrees for 1 hour. When 1 hour is up, turn off the oven 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 are up, remove the cheesecake from the oven and 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 cold, at least 8 hours. (I usually bake the night before and let it refrigerate overnight).
Once the cheesecake has chilled, carefully remove it from the springform pan and transfer it to a serving plate.