Preheat oven to 350 degrees F.
Toast the unsalted pistachios in the oven for 10 to 15 minutes or until crisp. Pull from oven, cool and finely chop. Place chopped pistachios in a bowl.
In the bowl of an electric mixer, whip the heavy cream with 1 tablespoon of sugar until it holds a soft peak. In a large bowl fold together the whipped cream, raisins, 1/3 of the chopped chocolate, 1/3 of the chopped pistachios and 1 tablespoon of sugar. Gently fold the whipped cream mixture into the ricotta. When ready to serve, spoon the filling into a pastry bag fitted with a fat round tip. Fill the cannoli shells from each end.
Blend the remaining chopped chocolate and pistachios on a plate.
To garnish: Dip each end of the cannoli into the chocolate pistachio mixture.
Cannoli can be filled and stored in the refrigerator no more than 1 hour ahead of time.