16. Dried Kaffir Lime Leaves
Dried leaves can be an interesting type of spice, although not all of them will have any significant taste. Dried kaffir lime leaves are a good example of a leaf that holds its flavor well. As you might expect, the leaves have a lime flavor. That flavor works particularly well in Thai dishes, although some Western dishes are also complemented by the extra flavor. Using these leaves as a spice can be especially appealing, because it lets you add in a lime flavor without any extra moisture. An alternative way to do that is lime zest, but the leaves are much more versatile.
Like ginger, galangal is a rhizome, and like ginger it tends to look ugly when you first see it. Telling the two apart is relatively easy though, as galangal has whiter and more shiny skin, and is much harder than ginger. You can find the spice ground, but this will only have a proportion of the flavor of the real thing. Instead, the best approach is to use the galangal root (if you can find it), and use a spice grinder to grind it up. Galangal is a relatively common ingredient in Indonesian and Malaysian recipes and can sometimes be found in stores specializing in Asian foods.
Mahlab is an interesting spice. The spice is actually the dried extracted kernel of a particular species of sour cherry. The spice can be used whole, but typically it is ground using a mortar and pestle or in a grinder. Mahlab has a nutty and sour flavor that some people find to be a combination of bitter almonds and sour cherries. This flavor can be used in sweet and in savory dishes. One example is adding a little of the spice to sweet bread, which helps to tone down some of the sweetness and add an interesting depth to the taste.