Chateaubriand (pronounced "sha-toe-bree-AHN") is a culinary term, which, like Delmonico steak, manages to convey meaning while remaining all but undefinable.
In fact, when defined broadly enough, the words chateaubriand and Delmonico steak could conceivably be used to refer to the same piece of meat. Indeed, some wonder whether either term refers to a specific cut at all, or rather a particular method of preparing it.
One thing that is clear about the word chateaubriand is that it refers to beef.
Still, even within the lavish tradition of culinary lore, an aura of particular extravagance surrounds chateaubriand, named for a 19th century French aristocrat named François-René de Chateaubriand, whose chef is said to have invented it.
According to legend, chateaubriand was a large, boneless cut of beef prepared by layering it within two or more lesser steaks, tying it into a bundle, then roasting or grilling it. When the outer steaks were charred, the roast was done, and the burnt outer steaks were then discarded. This technique supposedly ensured that the chateaubriand was cooked evenly throughout.
(It's a distinctly more extravagant variation on the technique of barding, where a piece of meat is wrapped in fat before roasting it.)
As if this were not decadent enough, chateaubriand was famously served with château potatoes, a dish prepared by trimming individual potatoes down to the size of olives, then sautéeing them in butter.
A historical footnote: the ultra-royalist for whom the dish is named died in Paris in the French Revolution of 1848.
Beyond the fact that chateaubriand today is no longer prepared by literally wrapping it in steak, there is little agreement about whether the word refers to a roast or a steak. Nevertheless, the interpretations fall into two main categories, depending on whether you're at a butcher shop or a restaurant.
1. Chateaubriand Is A Roast
According to this school of thought, chateaubriand is a roast made from the center section of the beef tenderloin and served with a white wine demi-glace sauce.
This chateaubriand preparation uses an approximately four-inch section of beef tenderloin, which is the most tender cut of beef. Because it's so thick, the chateaubriand must be roasted carefully to ensure it is properly cooked. (Hence the technique described above.)
Supporting this definition is the fact that butcher shops will often market a center cut beef tenderloin roast as chateaubriand.
(Beware, however, a roast taken from the butt end of the tenderloin which is described as a chateaubriand. Evidence of this deception is that almost invariably, this supposed chateaubriand will be tied together with butcher's twine, a step which would be wholly unnecessary for a true center-cut tenderloin roast.)
2. Chateaubriand Is A Steak
In this worldview, chateaubriand is a thick steak taken from the beef short loin, either a porterhouse or a T-bone.
This version of chateaubriand is generally grilled while basting it generously in butter (classical sources show that it was sometimes sautéed in butter). Traditionally served with something known as château sauce (essentially a variant on the Bercy sauce, but with the addition of lemon juice, tarragon and possibly mushrooms), modern chateaubriand is usually served with béarnaise sauce.