In a medium saucepan, combine milk, cream, remaining 1/4 cup sugar, cinnamon, and salt. Bring just to a boil over medium heat. Slowly whisk one-third of hot milk mixture into egg mixture. Transfer egg mixture to saucepan; cook, stirring constantly, until a candy thermometer measures 180°. Remove pan from heat. Strain mixture through a fine-mesh sieve into prepared bowl. Whisk in ricotta, mascarpone, vanilla extract, and zest until smooth. Let cool until mixture registers 40°. Transfer to refrigerator, and chill for at least 3 hours.