2 cups whole milk, divided
2 tbsp. cornstarch
1/3 cup sugar
7 oz. pistachio paste (I used closer to 5.5 oz)
A few drops of lemon juice
Combine ¼ cup whole milk with the cornstarch in a small bowl; whisk together to form a slurry so all the cornstarch is dissolved and the mixture is smooth. Combine the remaining milk with the sugar in a medium saucepan. Heat over medium-high heat, stirring occasionally, until the mixture is almost to a boil. Stir in the cornstarch mixture and cook at a gentle simmer for 3 minutes, stirring constantly. Remove from the heat, transfer to a bowl, cover and refrigerate until completely chilled, preferably overnight. Once the mixture is thoroughly chilled, whisk in the pistachio paste and a few drops of lemon juice. Freeze the gelato in an ice cream maker according to the manufacturer’s instructions. Store in an airtight container in the freezer.