Mahlab

Mahlab is the inner kernel of the St Lucie cherry stone, ground into a fine pale powder. It's a quietly common ingredient in Middle Eastern and Mediterranean baking - Persian love cake, Greek tsoureki, Lebanese ka'ak - where it lends a delicate flavour somewhere between bitter almond, sour cherry and a whisper of vanilla. Treat it like nutmeg: a quarter teaspoon goes a long way, and overdoing it produces a tannic, medicinal bitterness that overwhelms the rest of the bake. It oxidises quickly once ground, so buy whole kernels if you can and pestle them fresh, or use ground mahlab within a few months.