For the Streusel:

1. In a medium bowl, add the softened butter, brown sugar, flour, pumpkin pie spice, and a pinch of salt.
2. Mix everything together until it forms coarse, thick crumbs.
3. Place the streusel in the refrigerator to chill while you prepare the rest of the cheesecake.

For the Spiced Brown Sugar Filling:

1. Combine the brown sugar and pumpkin pie spice in a small bowl.
2. Whisk until well mixed and set aside.

For the Biscoff Crust:

1. Preheat your oven to 350°F (175°C).
2. Prepare a 9-inch springform pan by wrapping the bottom and sides with multiple layers of foil to prevent water from seeping in during baking.
3. Alternative method: Place the springform pan inside a 10-inch cake pan to avoid water leakage during the water bath (as explained in the intro).
4. In a food processor, pulse the Biscoff cookies until finely ground.
5. Add the melted butter and sugar, pulsing until fully combined.
6. Press the mixture firmly into the bottom and slightly up the sides of the springform pan (about 1 inch up).
7. Bake the crust for 15 minutes, then set it aside to cool while you prepare the cheesecake filling.

For the Pumpkin Cheesecake:

1. Reduce the oven temperature to 325°F (160°C).
2. In a large mixing bowl, beat the softened cream cheese and sugar together on medium speed until smooth and creamy.
3. Add the cornstarch and continue beating until well incorporated.
4. Mix in the pumpkin puree, sour cream, pumpkin pie spice, and vanilla extract. Beat on medium speed until smooth.
5. Add the eggs and egg yolks, one at a time, beating on low speed after each addition just until combined. Do not overmix.
6. Pour half of the cheesecake batter over the cooled Biscoff crust.
7. Sprinkle the spiced brown sugar mixture evenly over the first layer of cheesecake batter.
8. Pour the remaining cheesecake batter on top and smooth out the surface.
9. Sprinkle the prepared streusel over the top of the cheesecake.

Baking the Cheesecake:

1. Place the cheesecake in a large roasting pan and carefully pour hot water into the roasting pan, filling it halfway up the sides of the springform pan.
2. Bake the cheesecake for 1 hour and 15 minutes, or until the center is set but still slightly jiggly.
3. Turn off the oven and crack the oven door open slightly. Allow the cheesecake to cool in the oven for 1 hour.
4. Afterward, remove the cheesecake from the water bath and allow it to cool completely at room temperature.
5. Once cooled, refrigerate the cheesecake for at least 4 hours, or preferably overnight.

For the Whipped Cream:

1. In a mixing bowl, whip the heavy cream and powdered sugar together on high speed until stiff peaks form.
2. Serve the cheesecake slices topped with a dollop of whipped cream.