Dissolve the powdered sahlab or cornstarch in 1 cup of cold milk.

Mix very well until the mixture is quite smooth, ensuring no lumps remain.

In a large saucepan, stir the remaining milk and sugar together.

Bring the mixture to a boil over medium heat, stirring constantly to prevent scorching.

Add the sahlab/cornstarch mixture and mastic to the warm milk in the saucepan.

Simmer over medium heat, stirring constantly, until the mixture thickens and coats the back of a spoon.

The mixture should be slightly elastic at this stage.

Remove the pan from the heat.

Add the saffron-rose water mixture.

Mix well to evenly distribute the saffron and rosewater.

Allow the mixture to cool for 2 hours, stirring occasionally.

Pour the cooled mixture into an ice-cream machine.

Follow your ice-cream machine's directions for making ice cream. Typically this takes around 1 hour and 40 minutes.

Pour a thin layer of whipping cream into a flat plate.

Place the plate in the freezer until a 1/4-inch frozen creamy crust forms.

Remove the crust from the freezer and let it stand for 2 minutes to slightly soften.

Break off 1/2-inch pieces of the crust.

Mix the frozen cream pieces with the finished ice cream.

Transfer the ice cream to a press-in-lid plastic container.

Cover the container and keep it in the freezer to allow the taste to develop further.

Serve the saffron ice cream in small crystal bowls.

Sprinkle the top with ground pistachios for decoration.