Pour the cream into a 9-inch freezer-proof pie dish and place in the freezer. In a small bowl, dissolve the sahlab in 1 cup milk until quite smooth. Set aside. To make the ice cream: In a medium saucepan, bring 3 cups milk and the sugar to boil, and reduce heat to very low. Add the sahlab mixture, salt, saffron-rose water, and mastic, and bring back to a boil. Reduce heat to low and simmer, whisking constantly, for 10 to 20 minutes until thick enough for the mixture to coat the back of a spoon. Remove from heat and allow to cool then chill in refrigerator. Pour into a chilled ice cream maker and follow the manufacturer’s instructions for making ice cream (in my machine it takes about 1 hour 40 minutes). Remove the cream from the freezer. Un-mold it from the pan and break it into ¼-inch pieces. Add it to the ice cream in the machine. Add the pistachios and continue to turn in the machine for another 20 seconds. Pour the ice cream into a freezer-proof glass container with a press-in-place lid. Cover tightly (uncovered ice cream develops an unpleasant taste). Freeze the ice cream for at least 1 hour to allow it to develop texture and flavor. Twenty minutes before serving, remove the ice cream from the freezer and refrigerate. Serve by placing 3 scoops of ice cream into individual glass containers or use 2 wafers to make an ice cream sandwich.