Preheat oven to 350°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.