The short answer
Amlou is a sweet spread of almonds and argan oil, often called Morocco's almond-argan Nutella. You can taste it at the women's argan cooperatives on the roads out of Marrakech: our Ourika Valley, Three Valleys and Essaouira day trips all stop at one, where you watch argan nuts pressed by hand.
In more detail
Argan oil comes from the nut of the argan tree, which grows across the plains between Marrakech and the Atlantic coast. Pressed for the kitchen, the oil has a nutty flavour, and blended with almonds it becomes amlou, a thick, sweet spread eaten on bread at breakfast.
The cooperatives are the place to taste it. On the Ourika road, our day trip stops at a women's argan cooperative where you watch women press the nuts by hand and taste amlou. The Three Valleys loop includes an argan cooperative stop too. On the Essaouira road, the cooperative visit comes with argan pressing, amlou tasting and the famous goats in the trees.
The same cooperatives sell argan oil, for cooking and for skin, along with amlou to take home. Buy small, from a source you trust, and keep jars in your hold luggage.
Argan turns up in the city too. Oriental Legend, an ice-cream and pastry shop in the Kasbah, lists argan oil among its flavours, alongside Taliouine saffron and chebakia.