Tapioca with raspberries:
Heat the raspberry coulis and water in a saucepan, and as soon as the mixture comes to a boil, add the tapioca in a stream.
Reduce the heat to a simmer and cook, stirring frequently with a whisk, until the tapioca is cooked. It should be translucent, about 25 to 30 minutes.
Remove from heat and add the sugar. Mix well and let cool.
Divide half of the mixture into 6 glasses. Reserve.

Mascarpone with vanilla:
Beat the mascarpone, sugar, and vanilla with an electric mixer.
Divide 3/4 of the mixture into the glasses, over the tapioca with raspberries.
Add the remaining tapioca, then again, the remaining mascarpone.
Chill in the refrigerator until serving.