This is a recreation of a rubb (ربّ), or inspissated fruit juice, made with pressed and strained citron pulp, sweetened with sugar (though honey can also be used), and boiled down with a spice sachet of saffron and nutmeg. When it is ready, wait for it to cool down to drink. Though primarily a medicinal drink which, so the author assures us, is beneficial for all kinds of stomach ailments, it really can be enjoyed even for those who are spared those!
The 11th-century pharmacologist Ibn Jazla has a similar recipe, adding that it is even better if made with the peel, with the spice sachet containing ginger, cinnamon, cardamom, nutmeg, cloves and long pepper.
In Muslim culture, the citron is endorsed by a famous Hadith, according to which “the example of a believer who recites the Qur’an and acts on it, is like a citron which tastes nice and smells nice.”
It was praised in pre-Islamic times as well and in his book on ‘Prophetic medicine’, Ibn Qayyim al-Jawziyya (d. 1350)reported that one of the Persian Sassanid rulers was displeased with his physicians and ordered they be jailed, but he gave them a choice of food. They chose the citron and when queried by the monarch, they replied: “Because it quickly becomes a perfume, its appearance gladdens the heart, its peel is fragrant, the flesh is a fruit, the pith a food, and its seeds an antidote.