Prior to making this dessert, steep the raisins in enough Grand Marnier or orange liqueur to cover and leave for several hours (or overnight).
To prepare the custard: In a large saucepan, place the milk, cream, butter, sugar, cinnamon, vanilla bean and essence. Place over medium heat, stirring occasionally, until butter is melted and mixture is steaming hot. Do not allow to simmer or boil. Remove from heat, cover, and set aside to steep for 30 minutes.
To pre-cook the rice: In a large saucepan, combine the milk, rice and salt. Place over medium heat and bring to a gentle simmer. Continue to simmer, stirring frequently for about 6 minutes. Watch carefully, as this mixture has a tendency to want to boil over. Rice will be partially-cooked and slightly thickened. Remove from heat, cover and set aside until the custard is done steeping.
Once the custard has steeped remove and discard the cinnamon sticks and vanilla pods. After you have removed the vanilla pods from the custard mixture, stir the rice mixture into the custard mixture. Place on the stovetop over medium heat and bring to a simmer. Continue to simmer gently, for 30 minutes, stirring occasionally. Remove from heat, cover and set aside for 15 minutes, to cool slightly.
Drain all Grand Marnier/liquid from the optional raisins. Zest the orange. In a small bowl, using a fork, whisk the eggs. Place the drained raisins, and orange zest in the slightly-cooled rice mixture. In a slow, steady stream, stirring constantly, add the eggs. Return to heat and simmer very gently for 3 additional minutes.
Remove from heat, cover and set aside for 2-6 hours. Can be served warm or chilled.