Start by straining the ricotta cheese to remove excess liquid. This ensures your filling is thick and creamy instead of watery. Then, mix in the pistachio paste, powdered sugar, vanilla, and salt until smooth.
Transfer the filling to a pastry bag. Carefully pipe the pistachio cream into each shell just before serving to keep them crisp. Avoid filling too early, or the shells may become soggy.
Melt chocolate in a small saucepan or microwave. Dip the ends of the filled cannoli in chocolate, then coat with chopped pistachios. Let them set before serving.