For the Streusel:

1. In a medium bowl, combine the butter, brown sugar, flour, pumpkin pie spice, and salt. Mix until it forms coarse crumbs.
2. Place the streusel mixture in the refrigerator while preparing the rest of the cheesecake.

For the Spiced Brown Sugar Filling:

1. In a small bowl, whisk together the brown sugar and pumpkin pie spice. Set aside.

For the Biscoff Crust:

1. Preheat the oven to 350°F (175°C).
2. Wrap the bottom and sides of a 9-inch springform pan with multiple layers of tinfoil to protect it from the water bath. Alternatively, you can place the springform pan inside a 10-inch cake pan.
3. Pulse the Biscoff cookies in a food processor until finely ground. Add the melted butter and sugar, and pulse until combined.
4. Press the cookie mixture into the bottom and up the sides of the springform pan, about 1 inch high.
5. Bake the crust for 15 minutes, then let it cool completely.

For the Pumpkin Cheesecake:

1. In the bowl of a stand mixer, beat the softened cream cheese, granulated sugar, and cornstarch for about 2 minutes on medium speed until smooth and lump-free. Scrape down the sides of the bowl to ensure even mixing.
2. Add the pumpkin puree, sour cream, pumpkin pie spice, and vanilla extract. Mix for 1 minute on medium speed and scrape the bowl again.
3. Boil a pot of water for the water bath.
4. Add the eggs and egg yolks, one at a time, mixing on low speed until fully incorporated. Do not overmix.
5. Pour half of the cheesecake batter into the cooled Biscoff crust. Smooth the top with an offset spatula.
6. Sprinkle the spiced brown sugar filling evenly over the cheesecake layer.
7. Pour the remaining cheesecake batter on top and smooth it out. Sprinkle the chilled streusel on top.
8. Place the cheesecake in a large roasting pan. Carefully pour boiling water into the roasting pan, ensuring it comes about 1 ½ inches up the sides of the springform pan.
9. Bake at 350°F (175°C) for 1 hour and 30 minutes. If the streusel begins to brown too much, loosely cover the cheesecake with aluminum foil.
10. After baking, turn off the oven, crack the oven door open slightly, and let the cheesecake sit in the oven for an additional hour.
11. Remove the cheesecake from the oven and run a butter knife around the edges to loosen it. Allow the cheesecake to cool completely at room temperature, then refrigerate for at least 8 hours or overnight.

For the Whipped Cream:

1. Whip the heavy cream and powdered sugar together in a large mixing bowl until soft peaks form. Serve the whipped cream with slices of cheesecake.