Place the Biscoff cookies in a bowl and crush them with a rolling pin until they become fine crumbs.

Reserve two-thirds of the crumbs to mix into the mascarpone cream. Grind the remaining one-third into fine crumbs to sift over the top for decoration.

Soften 250g mascarpone cheese by letting it sit at room temperature. Stir until smooth and creamy in a mixing bowl.

In another clean bowl, whip 250g heavy cream with 10g sugar and 2g sea salt using an electric mixer. Whip until soft peaks form and the cream thickens.

Fold the reserved two-thirds of the crushed Biscoff cookies into the whipped cream gently. Then, combine this mixture with the mascarpone cheese, folding until evenly mixed into a creamy filling.

Quickly dip ladyfingers into espresso, ensuring they absorb some liquid but don't become soggy. Arrange a layer of dipped ladyfingers in the base of a shallow dish or baking tray.

Spread a portion of the prepared mascarpone filling over the ladyfingers evenly, smoothing with a spatula.

Repeat with another layer of dipped ladyfingers, followed by another layer of mascarpone filling.

Cover the tiramisu with plastic wrap and refrigerate overnight to let the flavors meld and the tiramisu set.

Before serving, sift the reserved fine cookie crumbs evenly over the top for decoration. If desired, add a sprinkle of butter crisps to enhance the texture and flavor. Cut the tiramisu into 6 portions and place one Biscoff cookie on each slice as the final touch.