In a small bowl or a 2-cup measuring cup, stir together the cornstarch and heavy cream using a fork, making sure there are no lumps. Place the milk and sugar in a saucepan and bring to a simmer, stirring so that the sugar dissolves. Remove from the heat and stir in the heavy cream mixture. Return the pan to the stove and cook over moderate heat, stirring constantly, until it thickens. It should coat the back of the spatula or spoon. Taste the mixture: make sure it does not have any floury taste, if it does, continue to simmer it until the cornstarch is cooked.
Remove from the heat and add the orange blossom water. Chill the mixture thoroughly in the refrigerator, then churn in your ice cream maker according to your manufacturer's directions.
Optional: Add 1/3 c. chopped pistachios toward the end of freezing.