Sauteed rex sole with spring vegetable salad in bacon vinaigrette

A fine plate of sand dabs is the kind of thing you can imagine the hero of a Raymond Chandler or Dashiell Hammett novel ordering, maybe at Musso & Frank in Hollywood or Tadich Grill in San Francisco. Just picture it: Simply sauteed or broiled in butter, the fish is delivered to a deep, leather-lined booth along with an icy martini or a bottle of the finest California “Chablis,� and then ceremoniously separated from its bones in two or three deft strokes by a white-jacketed waiter.

The hero takes a bite of the lean, minerally flesh, quaffs deeply of his drink and smiles before delivering a deadpan one-liner to the dame cuddled in beside him.

Unfortunately, even a detective as sharp as Philip Marlowe or Sam Spade would have a hard time tracking down a fresh sand dab today. Unless you’re willing to settle for frozen, this iconic California fish is exceedingly hard to find.

Not to worry. The ‘dab might be dead, but long live the rex. Rex sole, that is, a fish that is almost identical to the sand dab in all the most important ways. Its flesh is moist and firm, its flavor clean and sweet. Fry it or poach it, serve it simply with lemon and butter or gussy it up with a complicated cream sauce -- this fish is remarkably flexible.

Even better, it is among the most affordable in the market. While the newest, hottest wild salmon is going for $30 a pound, you can almost always find rex sole at $5 or $6.

First, though, don’t waste time mourning the ‘dab. This is no murder mystery. The sand dab isn’t really dead, just lying low due to recent changes in fishery regulations. In fact, you may not have even noticed it was gone; sand dabs and rex sole are so similar that some markets might be tempted to “confuse� the two and label the lesser-known rex as its more famous cousin.

If you’re curious, check the skin side of the fish: Sand dabs are brownish gray; rex sole is blackish gray. Other than that, it’s tough to tell.

Both sand dabs and rex sole are very small flatfish (whole fish average two or three to the pound). They’re so small, in fact, that they are very difficult to fillet. In the market they are usually sold in a form described as “pan ready,� which is two fillets joined to a central bone. These weigh anywhere from 2 to 5 ounces. Figure two per person for a main course; one will do for an appetizer.

Despite being extremely thin, the flesh is dense and takes heat well. You have to really overcook these fish to dry them out. Up to a point, the more well done they are, the better, as the fillet lifts more easily from the bone.

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A deep question

The most important difference between the two fish is that sand dabs are usually found in relatively shallow water -- they are most common between 120 and 300 feet -- while the rex sole is found slightly deeper -- up to 900 feet. That might not seem like much of a difference, but it is critical to commercial fishermen. A complicated series of regulations designed to protect threatened rockfish species has restricted various types of bottom fishing at less than 600 feet in many areas at different times of the year.

As a result, although both fish are plentiful in the ocean, according to the Monterey Bay Aquarium’s Seafood Watch program, fresh sand dabs are scarce in the markets, while rex is fairly common.

That’s the opposite of the way it was in the days of Chandler and Hammett, when sand dabs ranked right behind halibut as the most popular flatfish. More than 2 million pounds of sand dabs were caught in California in 1916, compared with less than 300,000 pounds in 2004. Rex sole wasn’t even tracked as a separate species until the 1930s, but it has certainly caught up: Landings in 2004 were nearly four times those of sand dabs.

Historically, the sand dab was highly concentrated in one port: Until after World War I, almost 90% of the catch was landed in San Francisco. This gave rise to a great tradition of ‘dab eating at the city’s many seafood grills, such as Tadich and Sam’s.

At these restaurants, there wasn’t much mystery in the cooking. The fish was usually treated simply, either broiled or served “meuniere� -- lightly dusted with flour and sauteed in hot butter. Prepared this way, the flesh develops a firm, meaty texture and, combined with a small sauce made from a little more butter and accompanied by a few steamed potatoes, this is where most traditional cooks leave it.

There’s certainly nothing wrong with that. But with a fish this good, why not try something different? Instead of plain potatoes, what about steaming a couple of other spring vegetables -- radishes and bulbing onions -- and then serving them as a kind of warm salad, dressed not with melted butter but with a tart, smoky bacon vinaigrette (yet another idea stolen from Thomas Keller’s wonderful “Bouchon� cookbook).

And why settle for sauteing? It turns out rex sole has a remarkably versatile flesh that adapts well to other kinds of cooking too. In fact, the way it varies with different cooking techniques is one of rex sole’s most interesting aspects. It is a fish with a thousand faces.

Poaching, for example, turns the flesh from meaty to moist. Cook rex sole with a little white wine and cream, surrounded by mushrooms above and below, and the fillets turn absolutely silky.

Or steam the fish, not by itself on the stove top, but in paper with other flavorings (parchment is the classic, but honestly, aluminum foil works better). Treated this way, the texture becomes somewhere between sauteed and poached -- firm but still velvety.

Lay a piece or two of rex on a sheet of foil, scatter sugar snap peas over the top and spoon some hazelnut- and lemon-flavored butter over everything, and you’ve got a terrific spring appetizer, which can be prepared well in advance and baked just before serving.

Wait until everyone is at the table to bring out the puffy foil packages. Then watch as the guests pop open these mysterious little gifts and are enveloped by the scented steam that billows out, the mingled scents of butter, hazelnuts, citrus and sweet sole meat.

Take a bite of the crunchy sugar snaps, then the silky fish. Swab up some of the butter and golden hazelnuts.

And that’s when it hits you. The only real mystery is why the rex sole isn’t better known already.

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How to deal with those tiny bones

Rex sole are so small that they are very difficult to fillet. Instead, you usually buy them “pan ready,� which means cut into pieces that look like fillets but have bones running down the center. These bones are easily removed after cooking.

Keep in mind that the bones look like a miniature fish skeleton, with a central spine and perpendicular pin bones springing from it. To remove the meat, cut a line down the center of the fish with a table knife, roughly along the main spine bone. Run the knife under half of the fillet and lift it off. Repeat with the other side.

Lift the very tip of the bone free of the underlying fillet and then carefully work the rest of it loose, lifting the spine with your fingers or a fork while separating bone from meat with the knife.

Do all of this with some care, as the bones are fragile and have a tendency to break apart.

The more well done the fish is, the more easily the meat will separate from the bones. Undercooking rex sole will result in a messy tug of war at the table. Fortunately, the fish handles extended cooking very well, so err on the side of caution.