Preheat oven to 325°F (165°C). Wrap the outside of a 9-inch springform pan in heavy-duty foil to prepare for a water bath.

In a bowl, combine the Biscoff cookie crumbs, melted butter, and salt (if using) until the mixture resembles wet sand.

Press the crust mixture firmly and evenly into the bottom and slightly up the sides of the springform pan. Bake for 8–10 minutes, then set aside to cool slightly while you prepare the filling.

To make the caramel sauce: Add the 1 CUP sugar to a heavy-bottom saucepan over medium heat. Cook, stirring occasionally, until the sugar melts and turns a deep amber colour.

Carefully whisk in the 6 TBSP butter until fully melted and combined. Slowly stream in the 1/2 CUP warm cream while whisking. Let bubble for 1–2 minutes, then remove from heat and stir in the flake salt. Let cool to room temperature.

For the filling: In a stand mixer, beat the cream cheese on medium speed until completely smooth, scraping the bowl as needed.

Add the 1 CUP sugar and beat until light and creamy. Mix in the sour cream and vanilla until smooth, avoiding adding too much air.

Add the eggs one at a time, mixing on low just until each egg is incorporated. Do not overbeat once the eggs are in.

Fold in 1/4 CUP of the cooled salted caramel sauce gently, so it is fully incorporated into the batter.

Pour the cheesecake batter over the baked crust. Tap the pan gently on the counter to release any large air bubbles.

Place the wrapped springform pan in a larger roasting pan. Pour hot water into the roasting pan until it comes about halfway up the sides of the springform pan to create a water bath.

Bake at 325°F for about 70–80 minutes, until the edges are set and the centre still has a slight jiggle. Turn off the oven, crack the door, and let the cheesecake cool in the oven for 45–60 minutes.

Remove the cheesecake from the water bath, run a knife around the edge, and let cool to room temperature. Then chill for at least 4 hours or overnight until fully set.

Before serving, gently warm the remaining salted caramel sauce if it has thickened too much, then pour or spoon it over the top of the chilled cheesecake. Finish with extra flake salt on top.