Brown Sugar and Cinnamon Ice Cream

I made 4 different kinds of ice cream in two days, and this was the ultimate favorite, across the board.
6 large egg yolks
2 cups heavy whipping cream
2/3 cup raw sugar
Pinch of salt
1 cup chilled buttermilk
1 teaspoon vanilla extract
1/4 cup brown sugar
1/4 tsp cinnamon

Whisk yolks in another medium metal bowl. Combine cream, sugar, and salt in large saucepan. Bring to simmer over medium heat, stirring until sugar dissolves. Gradually whisk half of hot cream into egg yolks, then return mixture to saucepan. Stir constantly over medium-low heat until custard thickens and coats back of spoon when finger is drawn across, 2 to 3 minutes (do not boil). Remove from heat.

Pour cold buttermilk into reserved chilled bowl. Strain custard into buttermilk; whisk. Whisk in vanilla. Chill mixture uncovered until cold, stirring occasionally, about 2 hours.
Stir in brown sugar and cinnamon until incorporated.

Process custard in ice cream maker according to manufacturer's instructions. Transfer ice cream to freezer container. Cover and freeze until firm, at least 6 hours or overnight.