I promise this won't become a sous vide blog.

Thomas Keller's Under Pressure: Cooking Sous VideSous vide, French for under vacuum, is a method of cooking that applies precise, low heat to food for relatively-long durations. The heat is transferred to the food through a water bath kept well below the boiling point; in professional applications, the water bath is accurately and precisely maintained at a given temperature via a thermal immersion circulator: essentially a heating element, thermometer, circulating pump, and a logic board to tie it altogether.
The food is not added to the water bath directly; instead, it is vacuum packed (cryovacked) in a food and heat-safe plastic bag. The seal is airtight, even pressurized.
Every other form of cooking centers on how long heat is applied to the food. The heat is hotter than the food needs to cook: meat might need to reach an internal temperature of 135°F, but boiling water is 212°F (at standard atmosphere), your saute pan might be 300°F, your oven 400°F. Thus, to perfectly cook something is to time its subjection of high heat down to the second. Even still, to get the inside to a safe 135°F, the outside is going to be 250°F, with a "bulls-eye" gradation in temperature from the over-cooked surface to the (hopefully) properly-cooked interior.

Harold McGee: "This book introduces American cooks to one of the most important culinary innovations of modern times. A way of heating foods precisely. At last!"Sous vide turns that calculus on its head. With sous vide, the question isn't how long at this too-hot temperature but simply to what temperature? You can cook pork to a perfectly uniform medium-rare—say, 142.0°F. Vacuum seal the pork, perhaps with some herbs, set your thermal immersion circulator to 142°F, and drop the bag in the water bath. Two hours later, every cubic inch of the pork is exactly 142°F. Of course, it will take some experimentation (or handy premade sous vide charts) to find out how long it takes a given thickness and type of food to reach uniform temperature. But with sous vide, you can overshoot, as it is hard to overcook food. As any first year chemistry student can tell you, once the food and the bath are equal temperatures, cooking stops. (I say it is hard, but not impossible, to overcook with sous vide because not all elements of the food actually reach temperature, and after 48 hours of cooking you'll start to unacceptably break down the food.)
Sous vide is not perfect. As with any anaerobic environment, vacuum sealing poses a risk of botulism. And the temptation to scantly cook meat should not override the need to bring it above the "danger zone." Yet the biggest flaw is texture. That over-application of heat, while a problem, does give food a wonderful char, caramelization, and the Maillard reaction. So we often finish food cooked sous vide on the grill or in a saute pan, not to cook it further but to lend texture and caramelization to the exterior.

Sous Vide Strip Steak with sauteed pea shootsSous vide is nothing new, having been invented in a French kitchen in the 1970's, but it hit a sort of apex over the last year or two, culminating in the publication late last year of Chef Keller's Under Pressure. Today, you'd be hard pressed to find a serious restaurant that doesn't employ sous vide in some form for many, if not most, of its dishes. That's right: This weird bag thing is how they cook in professional kitchens. The ease and flexibility of cooking, the leeway in cooking times, the ability to consistently cook meat and vegetables perfectly, and the new found creative outlet, have all cemented sous vide into the arsenal of the professional chef. As with the immersion blender, its popularity is now gaining in home kitchens.
While you can do sous vide at home with a stockpot, stove, candy thermometer, and ziplock bags, professionals kitchens use an accurate thermal immersion circulator and a chamber-based vacuum sealer. Almost universally, chefs choose the PolyScience Thermal Circulator. For chamber vacuum sealers, Koch, Multivac, and PolyScience all produce popular models. For home use, a FoodSaver vacuum sealer works quite well, although it is hard to vacuum seal liquids without a chamber-based model.
For me, sous vide is exciting because it opens up a new method of cooking: One that brings an engineer's level of precision to the table. I've braised every tough cut of meat I could find; now I have a new skill to perfect. Sous vide, for example, let's you cook short ribs to barely medium rare. Or cook delicate fish without fuss. Or get creative, as in Under Pressure's "Vegetarian Steak Tartare:" Compressed Watermelon and Hayden Mango Yolk.
As with any tool or technique, sous vide has its place. Not to be overused, but not to be outright rejected, either. One excellent application is the precise cooking of thick cuts of steak to a perfect, uniform medium-rare, without the addition of any fat or the loss of any juice. This recipe is for just that: the perfect steak.
Makes 1 steak.
Ingredients:
1 top-loin strip steak, about 1.5" thick, preferably dry-aged, trimmed of gratuitous fat
1 tablespoon grape seed oil
1 teaspoon fresh thyme
kosher salt, to taste
freshly-ground black pepper, to taste

Two top-loin strip steaksLet the steak sit at room temperature for at least 30 minutes. Liberally season with salt and pepper.

Vacuum packed on mediumVacuum pack the steak on medium.

Set to 130.9°F (not 134.1°F)Set your thermal immersion circulator to 130.9°F.

Cooking in a pot with the thermal immersion circulatorOnce to temperature, add the steak and cook for 90 minutes.

Out of the thermal immersion circulatorRemove the vacuum bag from the immersion circulator and remove the steak from the bag. Reseason both sides of the steak with salt and pepper.

Flipped, topped with thyme, and searing on the other sideHeat a skillet over medium-high heat. Add the grape seed oil. Once very hot, add the steak. Raise heat to high. Sear 60 seconds per side, until nicely browned. When you flip the steak over, garnish the just-seared side with fresh thyme.

Plated with sauteed pea shoots and ready to serveServe immediately, with greens of your choice. Pairs well with a big, bold, dusty Cabernet Sauvignon from the Rutherford district in California's Napa Valley.