Line the bottom of the baking pan with an even layer of cookies (use half the package or 16 cookies).
Mix the mascarpone cheese, sugar and Biscoff spread thoroughly with a spoon into a uniform and smooth mixture.
Whip heavy cream until it has consistency of whipped of cream. Gradually fold it into the mascarpone mixture, one-third each time, until you get a uniform mixture.
Pour half of the mixture on the cookie base and smooth it out with a palette knife. Cover with another layer of cookies, pour over the rest of the filling and smooth it out again. Cover and refrigerate overnight.
You can keep your tiramisu covered in the refrigerator for about 4 days. Before serving, sprinkle cocoa powder on the cake.
Ingredients for a rectangular pan 20cm x 30cm (8" x 12") in dimensions:
1 package of Biscoff Family Pack (8.8 oz) or 32 cookies