Toast the shelled pistachios in a skillet over medium heat for 3-4 minutes until fragrant and slightly golden. Cool and chop half for the mousse, reserving the rest for garnish.

In a mixing bowl, combine the pistachio paste, mascarpone cheese, powdered sugar, vanilla extract, and salt. Beat with an electric mixer on medium speed until smooth and creamy, about 3-5 minutes.

In a chilled bowl, whip the cold heavy whipping cream at high speed for 3-4 minutes until soft peaks form.

Gently fold one-third of the whipped cream into the pistachio mixture, then add the remaining whipped cream and chopped pistachios, folding until no streaks remain.

Divide the mousse mixture into serving glasses, cover with plastic wrap, and refrigerate for at least 3 hours or overnight.

Before serving, let the mousse sit at room temperature for 5 minutes, then garnish with reserved chopped pistachios.