In a medium saucepan over medium heat, add granulated sugar and stir continuously until it melts into a rich amber color, about 8–10 minutes. Whisk in unsalted butter until melted, then slowly pour in heavy cream and mix until smooth. Add vanilla extract and fine sea salt, combine well. Set aside to cool.

Preheat your oven to 350°F (175°C) and line the bottom of a springform pan with parchment paper. Mix crushed Biscoff cookies with melted butter and a pinch of salt. Press firmly into the bottom of the prepared pan, then bake for 8 minutes.

In a bowl, beat cream cheese and sugar together until smooth and creamy, about 3-4 minutes. Gradually mix in vanilla extract and cornstarch. Add eggs one at a time, mixing just until combined. Fold in sour cream, heavy cream, and cooled salted caramel.

Pour the filling into the cooled crust. Place the springform pan in a roasting pan and pour hot water until it reaches halfway up the sides. Bake at 325°F (163°C) for 75–85 minutes until edges are set but the center jiggles slightly.

Turn off the oven and crack the door open, allowing cheesecake to cool for 45–60 minutes. Let it cool to nearly room temperature before transferring to the refrigerator. Chill for at least 8 hours or overnight.

After chilling, remove the springform ring. Gently warm remaining salted caramel sauce until pourable, drizzle over cheesecake and sprinkle with flaky sea salt. Chill for an additional 15–20 minutes before slicing.