1. In place of onions: Substitute white parts in recipes (such as stir-fries and casseroles) to add a sweeter, more delicate flavor.
2. Throw in the dark green tops (discarded in most recipes) when making chicken or vegetable stock.
3. Put a layer of trimmed, halved, and rinsed leeks in a baking dish. Pour in white wine or chicken broth to come halfway up leeks. Add salt and pepper; dot with butter. Cover; bake at 375° until leeks are tender, about 45 minutes. Sprinkle with bread crumbs and shredded Gruyère cheese; bake, uncovered, until browned.
4. Chop white and light green parts and sauté in a little olive oil and garlic. Add chicken broth and some chopped potato; simmer until potato mashes easily. Purée in a blender and return to pan. Add a little whipping cream, salt, and pepper; heat until steaming.
Halved leeks: Trim off tough green parts, cut remaining portion in half lengthwise, and hold under cold running water, flipping layers to rinse out grit.
Chopped leeks: Cut off root ends, then quarter lengthwise through white and light green parts, leaving dark green tops intact. Using the tops as a handle, fan out light parts under running water and wash off grit.