Remove the seeds from the cardamom pods, transfer to a mortar and pestle. Pound them to a fine powder and set aside.
Add milk in a heavy-bottomed pan, add cream, followed with cornstarch, and sugar. Using a wire whisk, whisk the mixture very well. Make sure the cornstarch is not settled at the bottom of the pot {You may mix the cornstarch with about 1/2 cup of milk and then add the cornstarch slurry to the milk mixture too, but it doesn't make much of a difference if you use a wire whisk to mix up everything}. Then, switch on the flame to medium heat.
Cook the mahalabia pudding mix on medium heat, while continuously whisking the milk mixture until it begins to thicken, like a custard. This will take around 8-10 minutes. Do not stop whisking, or else the cornstarch will settle at the bottom and burn, or the mixture may turn clumpy. Continuous whisking until thickened is the only important step you need to follow while making this pudding.
As you continue whisking, you will see the mixture thickening up. Reduce the heat to low, and continue whisking. When it coats the back of a spoon, it is done.
Remove the pot off the heat, add the flavorings like rose or orange blossom water and freshly crushed ground cardamom (if using). Set aside to cool down for about 5 minutes.
Pour the mahalabia mixture into desired serving glasses or bowls, or one big bowl. I added some ground pistachios at the bottom of each glass, which is totally optional. Cover the glasses with a cling wrap or aluminum foil, chill in the refrigerator for 5-6 hours or overnight for best results. Garnish this delicious Middle Eastern milk pudding with rose syrup and chopped pistachios.