Pistachio Gelato

Bring 3 cups of the milk to a simmer in a medium saucepan over medium heat, then remove from heat. Combine remaining 1 cup milk, sugar, and cornstarch in a bowl, then stir into hot milk. Return pan to heat and cook, stirring constantly, until mixture thickens slightly, 8-10 minutes.

Put pistachios into a large bowl and stir in hot milk mixture. Set aside to let cool, stirring often, then cover and refrigerate overnight.

Strain mixture through a fine sieve into a bowl, pressing ground pistachios with the back of a wooden spoon. Discard pistachios. Process mixture in an ice cream maker according to manufacturer's directions.