In a small bowl, whisk together the Cornstarch and a little cold Whole Milk until you have a smooth, lump-free slurry.
Pour the remaining Whole Milk into a saucepan and warm over medium heat; stir in the Granulated Sugar until dissolved and the milk is steaming but not boiling.
Slowly pour a few spoonfuls of the hot milk into the cornstarch slurry to temper it, whisking constantly, then return the slurry to the saucepan.
Reduce the heat to low and cook, stirring constantly, until the mixture thickens and coats the back of a spoon—this usually takes a few minutes. Be patient and keep the heat gentle to avoid curdling.
Remove the pan from the heat and stir in a small splash of Orange Blossom Water and a touch of Rose Water to taste; these should be used sparingly so their aromas remain subtle and floral.
Pour the pudding into individual serving dishes or a shallow dish, smooth the tops, and let cool to room temperature.
Chill in the refrigerator until fully set, at least a couple of hours.
Before serving, sprinkle chopped Unsalted Pistachios over each portion for color and crunch.
