Instructions: STEVE JOHNSON, the chef at the Blue Room in Cambridge, Mass., has been cooking skirt steak for years, long before it became wildly popular. But never before has he served a better, or simpler, rendition of this long, thin band of wonderfully marbled beef.

His secret: a slice of compound butter, flavored with shallots, chives and thyme, that melts over the meat.

Until butter became a forbidden food, it was common as a flavor booster. In classic cooking, compound butters were kept on hand and often used to enhance rich sauces. But more recently, they have become more common on their own, topping not only steak, but also leaner meats like veal and chicken, and even fish. (And their side dishes, too: Place a little flavored butter on plain rice or steamed carrots and youll be considered brilliant.)

Compound butters are easy to make, and as Johnson pointed out, they can be frozen and used as needed, allowing a home cook to develop and execute signature dishes on the spot. Just form the butter into a log, wrap it well, freeze it and cut slices for anything grilled, broiled or even steamed. Start with unsalted butter (any good brand will do fine, as long as it is fresh). Compound butters can be made with various seasonings. At this time of the year, fresh herbs are a good candidate - chervil, dill and parsley are all nice - and roasted garlic puree can be sensational. Mustard, ginger, vinegar, chilies or citrus juice and zest work well, too. Seasonings can also be combined. A teaspoon each of horseradish or wasabi, ginger and soy sauce can be mixed into a stick of butter (add salt and pepper sparingly). Or add a teaspoon each of minced garlic, fresh oregano and lemon juice (add salt and plenty of ground black pepper, and if you are using roasted garlic, increase the quantity to 1 tablespoon). Other combinations include chili-cilantro: for each stick of butter add one small stemmed, seeded and minced chili, a tablespoon of minced cilantro and a teaspoon of lime juice, along with salt and ground pepper.

Cream the flavorings

The simplest way to make a compound butter is to mince the flavorings and cream them with the butter, using a fork. Butter that is slightly soft is best, but if it is cold (or frozen), use a small food processor. Youll never get all of the butter out of the container and blade, but the process will take just seconds.

Cut from the cows diaphragm, skirt steak is juicy and flavorful but not exactly tender; its chewier than good strip steak and does not respond well to overcooking. If someone at the table insists on having it cooked beyond medium-rare, even the compound butter wont save it.

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