If there’s one ingredient that says “Moroccan cooking” it’s preserved lemons. They’re smaller than most lemons found in the U.S. and also sweeter. Traditionally preserved in salt and lemon juice, they are used in tagines, stews and other dishes after the lemons have had time to sit in a tightly sealed jar for several weeks.
Once the jar is opened and lemons are ready to be used, the lemons can be cut open and used whole, although only the rind is typically used to add flavor in cooking. There’s nothing else like them. They can be hard to find in some places, but your best bet is at Middle Eastern / Mediterranean markets, specialty food stores, and online at Amazon.com. My favorite brand is the Les Moulins Mahjob, a Tunisian brand that adds a pepper to the mix of lemons, but a more economical yet just as good version is the Mina one, an authentic Moroccan brand that does this sort of thing quite well.