The Vietnamese wrap beef in these leaves, while others chew them like gum. It's sometimes used as a cooking green in Southeast Asia. Unlike regular chives, these have flat leaves and a distinct garlicky flavor. They're usually marketed and cooked before the buds open. It's fairly pungent, so it's rarely eaten raw.
Most Thai recipes count each double leaf as two separate leaves.
Frozen kaffir lime leaves are a good substitute for fresh. Dried leaves are much less flavorful, so use twice as many as the recipe calls for if you're substituting them for fresh leaves. It has a strong, minty, peppery flavor. It's sold in bunches with lots of pointy leaves on each stem. Thai cooks toss it into soups, salads, and noodle dishes.