Blend the biscuits and flavour with 2-3 spoonfuls rum. Press into the base of 4 glasses and refrigerate for at least 15 minutes. Cream the mascarpone, Piave cheese, scraped seeds of half a vanilla pod and 2 spoonfuls of sugar.
Spread the cream over the biscuit crumb base and return to the refrigerator for another 15 minutes. Blend the raspberries with a spoonful of sugar and either (to make a raspberry sauce rather than dressing) or add as-is.