Prepare a form with removable walls (products are for 10 1/4″ (26 cm) diameter tray). Put a layer of biscotti at the bottom after dipping them in sweetened milk, then start forming the walls by breaking each biscotti into 2 and arranging.
Once ready, put generous amounts of one cream (prepare it as described on packet), arrange a layer of biscotti and end with cream of the other color.
Another option is to spread white cream on half the cake, brown on the other half and use a spoon to make streaks to merge them.
Leave cake to sit in the fridge overnight for the creams to harden and for the biscotti to soak in the creams.