This is a handy, fat-free way to use up leek trimmings. Consider it a general guide, not a strict recipe. Cilantro or parsley stems are a pleasant addition, but not necessary. Add other aromatics: bits of celeriac, parsley root, parsnip, carrot, or dried mushrooms. Toss in shrimp shells for sweetness. Ignore the garnish and use the broth as a soup base; or freeze it for future soup-making.