Wash the rice in a mesh-sieve strainer under running cold water, transfer to a pot and add 3 cups of water, bring to a boil, reduce heat to very low cover up and cook for 25 minutes, remove from heat and set aside.
In a small bowl, dilute together 1 cup of milk (should be at room temperature) with the cornstarch, whisk well to homogenize, set aside.
In another pot, heat 6 cups of milk over medium high heat, whisk constantly and bring to a gentle boil, add the cooked rice and stir well to infuse together.
Bring to a boil, add the sugar, whisk the riz bil haleeb one more time, and reduce heat to very low, keep it simmering uncovered until the rice starts to float on top, about 5 minutes, add the heavy cream and the zest of 1 lemon, if used,( zest the bright outer yellow layer, and avoid the bitter white layer underneath) stir one more time, and simmer for further 5 minutes over low heat.
Stir in the diluted cornstarch, whisk well and bring to a boil one last time, simmer over low heat for further 5 minutes to cook out the starchy taste.
Add the orange blossom water, stir well, and remove the pot from heat, and our rice pudding aka riz bil haleeb is ready.
An indication that the consistency is perfect: Dip a metal spoon into the hot rice pudding and pull it out. Run your finger down the back of the spoon, if a clean, clear line stays without the liquid running, your riz bil haleeb is ready.
Laddle the rice pudding in the ramekins,
Optional step: To achieve the wrinkled top surface in riz bi haleeb, laddle it in ramekins while it’s still hot, and give each ramekin a squirt of water, the uneven temperatures create a shrink on top of the surface which looks like those favored wrinkles, yes, it’s an indication to many that your riz bil haleeb is authentic,
Serve it warm or right from the fridge.
You can garnish each ramekin with some chopped pistachios upon serving, optional.