Fleur de sel is a delicate white salt from the northern Atlantic coast of France, harvested by skimming the top of the evaporating sea water in salt marshes. Its name ("flower of salt" in French) comes the aroma of violets that develops as the salt dries.
Substitute any flaky sea salt (such as Maldon sea salt).
Fleur de sel can be slightly ivory or even grayish, depending on the minerals in the area it was harvested. It's usually sold in jars because it can be a little damp. If possible, sample a few kinds to see which you like best.
Do not waste this expensive, high-quality salt in pasta water or even to season meat before cooking. Instead use it as a finishing salt. Sprinkle sparingly to finish simple seafood (pan-roasted salmon, seared scallops), rare lamb, pork tenderloin, seared foie gras, simple summer tomato salads, or even chocolate or caramel desserts.
Store tightly covered.