Bastani Sonnati (Persian Saffron Ice Cream)

Crush the saffron threads and mastic together to a fine powder in a mortar and pestle.

Whisk the egg yolks with a little of the caster sugar in a mixing bowl until pale.

Heat the milk, remaining caster sugar and salep powder in a saucepan, stirring, until steaming but not boiling.

Pour a little of the hot milk onto the egg yolks, whisking constantly, then pour the mixture back into the pan.

Cook over low heat, stirring constantly, until the custard thickens enough to coat the back of a spoon.

Stir in the double cream, the crushed saffron and mastic, and the rosewater, then strain the custard into a bowl.

Chill the custard in the refrigerator until completely cold.

Pour the cold custard into a loaf tin and freeze, whisking vigorously with a fork every hour for the first four hours to break up the ice crystals, then freeze until firm, at least six hours or overnight.

Scoop into bowls and scatter with the chopped pistachios to serve.