Mix together the coffee and water then set aside to cool. In a microwaveable bowl, melt the biscoff spread in the microwave at 30 second increments until fully melted. Set aside to cool down.
Add the double cream to a stand mixer fitted with a whisk and whisk the cream to soft peaks. Add the mascarpone and melted biscoff spread and continue to whisk until it reaches medium to stiff peaks. You can also use a hand whisk for this process. Do not over mix. If in any doubt just stop mixing. You want the cream to be soft and fluffy.
Take one biscuit and lightly deep it into the coffee. Do not soak or the biscuit may get soggy and fall apart. Place the dipped biscuit in the base of a dish that measures around 8 x 8 inches and repeat the dipping process creating a layer of biscoff. As the biscoffs are quite thin, I create a second layer directly on top of the first layer with more biscoffs dipped in coffee.
Take half the cream and spread it onto the 2 layers of biscoff and use a palette knife to smooth it out. Repeat the process of dipping the biscoff into coffee and creating two more layers on top of the cream then spread the second half of the cream onto the two layers of biscoff biscuits.
Refrigerate for a minimum of 4 hours then finish off with some crushed biscoff sprinkled on top just before serving. Optionally, you can also melt more biscoff spread to drizzle on top when serving.