Mash 12.5 oz (350 g) of biscuits, break the rest into small pieces. Put them in a bowl. Melt the butter and while still warm, pour it over the biscuits.
Mix everything by hand and use plastic wrap to shape a roll. Put it in the freezer to harden.
Beat the confectionery cream with the powdered sugar and smear it on the now hardened roll. Finally, sprinkle with ground walnuts. Store the roll in the fridge.