Preheat your oven to 350°F (175°C). In a food processor, grind Biscoff cookies until fine crumbs form, then combine with melted butter in a mixing bowl. Press this mixture firmly into the bottom of a 9-inch springform pan. Bake for 10 minutes and allow to cool.

In a medium saucepan over low heat, add granulated sugar and stir until it melts and turns golden, about 8-10 minutes. Add unsalted butter and warm heavy cream, whisking until smooth. Stir in sea salt and let it cool.

In a mixing bowl, beat cream cheese, granulated sugar, and vanilla extract until smooth. Gradually add eggs, mixing well. Then, add heavy cream, sour cream, cornstarch, and half of the cooled caramel sauce until combined.

Pour the cheesecake filling into the cooled crust, smoothing the top. Bake at 325°F (160°C) for 70-75 minutes, or until the edges are set but the center is jiggly. Let it cool in the oven for 1 hour.

Chill at room temperature for another hour, then refrigerate overnight. Before serving, remove from the pan and drizzle with remaining salted caramel sauce and sprinkle with flaky sea salt.