1. – In a medium saucepan, heat 1 cup of heavy cream and 1/4 cup of sugar over medium heat, stirring occasionally, until the sugar has dissolved and the mixture is hot but not boiling.

2. – In a separate bowl, whisk the egg yolks. Slowly pour in the hot cream mixture, whisking constantly, to temper the yolks.

3. – Return the mixture to the saucepan and cook over medium heat, stirring continuously, until the mixture thickens enough to coat the back of a spoon, about 5-7 minutes.

4. – Remove from heat and stir in the chopped pistachios. Pour the mixture into a clean bowl and refrigerate for at least 2 hours, or until completely chilled and set.

5. – In a small saucepan, heat the 1/2 cup of heavy cream over medium heat until simmering. Remove from heat and add the chocolate chips. Let stand for 2-3 minutes, then stir until the chocolate is melted and the mixture is smooth. Allow to cool slightly.

6. – Using a hand mixer or stand mixer fitted with the whisk attachment, whip the chilled pistachio mixture until light and fluffy, about 2-3 minutes.

7. – Spoon or pipe the pistachio mousse into individual serving dishes. Drizzle the warm chocolate ganache over the top.

8. – Refrigerate for at least 30 minutes before serving. Garnish with additional chopped pistachios and a mint sprig, if desired.