This is an unusual spice that is a favourite in Middle Eastern baking, particularly at Easter. Mahlab or mahleb are the seed kernels of a black cherry tree that may have first grown around the Mediterranean. In fact the ancient Lebanese city of Mahalep is mentioned in the Bible.
The fruit of this plant is similar to a sour cherry. The tree can grow to 35 feet and is very hardy. It resists deseases and insects. The root stock of this plant is often used to graft less vigorous North American cherry trees.
Mahlab seeds have a slight bitter almond flavour. Many recipes suggest subsituting almonds or even anise for them but many pastry bakers look for mahlab to add an authentic flavour to Armenian Cheoreg (coffee rolls), Greek Lambropsomo (Easter Bread), and Syrian Ma'amoul (date or nut filled pastries).
The seeds should be ground just before adding their flavour to a recipe because the nutty aroma will dissipate very quickly. Don't buy it powdered unless you are sure that it smells fresh. An easy way to grind these seeds is by mixing in a little of the sugar or salt that is bound to be called for in the recipe. Use a mortar and pestle. The salt or sugar granules will quickly break down the mahlab seeds into powder.
Anatol, at 6822 St. Laurent boulevard (276-0107) is one of the few spice stores I have found that regularly carry Mahlab.
Here is a recipe for Cheoreg based on one from Treasured Armenian Recipes:
Mix a cup each of warm milk and melted butter. Add two beaten eggs, a tablespoon of yeast. Mix this well. Grind together a half teaspoon each of anise and mahleb with a teaspoon of salt. Add this to the liquid. Add 3 tablespoons of sugar. While mixing, add enough flour (about 6 cups) to make a soft dough. Knead it until it is smooth. Cover the dough and let it rest in a warm place, such as an oven with the light turned off, until it doubles. Roll out finger length pieces into strips about 8 inches long. Shape these into circles. Put them on an oiled cookie sheet. Brush the tops with another beaten egg. Sprinkle the tops with sesame seeds or chopped nuts if you want. Let them stand for 2 hours. Bake them in a 350 degree oven until golden brown for about 20 to 25 minutes.