Boil the shelled unsalted pistachios in a pot of water for 2 minutes. Drain and cool them.

Blend the blanched pistachios and whole milk in a high-speed blender for about 2 minutes until smooth.

In a saucepan over medium heat, whisk together corn starch and milk until dissolved, then add to the pistachio-milk mixture and heat until thickened.

Remove from heat, whisk in sugar, remaining milk, salt, and pistachio extract, then fold in heavy cream.

Chill the mixture in a bowl for several hours or overnight before churning in an ice cream maker.

After churning, scoop gelato into an airtight container, cover with parchment paper, seal, and freeze for at least 4 hours.