Chefs have thrown away the rulebook on what can go on a bun.

By Scott Hume, Special to R&I -- Restaurants and Institutions, 10/29/2009

At chic Terzo Piano cafe (Bon Appétit Management Company) in the Art Institute of Chicago, five-year-aged vinegar dresses a salad of roasted acorn squash and pear, and locally made chorizo tops flatbreads with manchego cheese.

Yet even on a menu as refined as this one, there's room for burgers—three, in fact, only one of which is made with beef. In addition to a burger featuring a Piemontese beef patty, Terzo Piano's Uno, Due, Tre trio includes a lamb burger topped with goat cheese and a shrimp burger with Calabrian-pepper spread.

Now that restaurants of all styles and price points menu burgers, chefs are going beyond the traditional, and often beyond beef, to stand out. In this realm in particular, there is no shortage of creative ideas.

“We like to do twists on the classics, not something someone could do at home,” says Duskie Estes, chef at Zazu in Santa Rosa, Calif., where wild-boar burgers are served with house-made sauce. Sister restaurant Bovolo in Healdsburg, Calif., menus a burger that's made from Duroc pork, a heritage breed, and topped with local-apple marmalade.

A new wave of upscale fast-casual chains has accelerated the movement toward nontraditional builds. Angus and Kobe beef are on the menu at Square One Burgers in Tampa, Fla., but other patty choices include bison, portobello mushroom and sashimi-style tuna. Santa Monica, Calif.-based chain The Counter features a different offbeat burger monthly, usually with a nonbeef patty. In October, it was a halibut burger topped with spicy jicama, roasted red peppers, baby greens, Bermuda and green onion, and chimichurri sauce.

VEGETARIAN

The Counter, multiple locations

Veggie Burger: Hand-formed patty of brown rice, spinach, mushrooms, corn, Panko breadcrumbs, zucchini, carrots, black beans and red bell peppers with choice of toppings (Approx. $8.25)