1/2cup finely chopped black walnuts (or English walnuts)
Beat egg yolks and sugar with electric mixer until thick and pale, about 2 minutes. Set aside.
Combine cream and milk in a medium saucepan; heat over medium-high heat until tiny bubbles form around the edge of pan (about 180F,) stirring often. Add one-third of the hot milk mixture to egg mixture, stirring with a whisk; slowly add mixture back to pan, stirring constantly with a whisk. Cook, stirring occasionally, over medium-low heat until mixture coats the back of a spoon, about 4 minutes. Remove from heat. Stir in vanilla. Cover and refrigerate until chilled, at least 1 hour.
Pour mixture into canister of ice cream maker and freeze according to manufacturer’s instructions. During the last few minutes of churning, add black walnuts. Serves 9.