The hamburger is moving up in the world.

A staple of the all-American meal, it's always been the taste of summer, barbecues and the Fourth of July — and the hottest item at fast-food restaurants and greasy spoons. But now, it's so much more.

The hamburger has gone all fancy on us, made with quality beef like Kobe and Angus, wedged in a brioche rather than a sesame-seed bun, topped with exotic fixins like goat cheese, Roquefort, avocado, caramelized onions and fois gras. Gone are the lettuce, tomato and slice of American. Ketchup? Don't ask.

Suddenly, le hamburger is among the appetizers and entrees offered at the finest restaurants across the country.

"It's a huge trend. We're seeing it at just about every level in the restaurant industry," said Barb Stuckey, a vice president at food and beverage innovator Mattson & Co. "It just started mushrooming. You've got the low end moving upscale: really good burgers at really good prices."

The high-end burger is sizzling so much that celebrity chef Laurent Tourondel, who founded the BLT restaurants, has one New York City eatery dedicated specifically to the old favorite, called BLT Burger.

The menu has variations on the basic beef sandwich that Americans love so much, made with four different cuts of Kobe or Black Angus and offering a choice of toppings including avocado, roasted red peppers, Portobello mushrooms, homemade chili, blue cheese and barbecued onions.

For those craving a burger made with something other than beef, Tourondel offers a lamb variety topped with cucumber, yogurt sauce and olives, and a salmon concoction dressed with avocado, red onion and tartar sauce, to name a few. And for breakfast, well, there's an egg burger, of course.

"It's a great evolution," Tourondel said. ""It's what people want to eat … My burgers are not too expensive, not too big and you're not too stuffed. You have a burger that can fit in your mouth and is not falling all over the place."

It's also a burger that can fit into your budget, ranging in price from $7 for the veggie variety to $16 for one made with Kobe beef at BLT. Most high-end hamburgers cost between $6 and $25, though BLT Burger tried charging $62 for one made with Japanese Kobe beef before ultimately taking the item off the menu.

In addition to offering a swankier hamburger as an entrée, many higher-end restaurants also feature a plate of mini burgers — or sliders — as an appetizer.

Tourondel's restaurant Brasserie Ruhlmann, also in Manhattan, is among the many haute-cuisine eateries to serve the minis as either a starter or a stand-alone dish. And the trend is spilling over into weddings, with the bite-sized versions served more frequently as hors d'oeuvres at receptions.

In San Francisco, rnm has mini burgers with caramelized onions and Vermont white cheddar, and Zuni Café is well-known for its house-ground hamburger on rosemary focaccia with aioli and a choice of gorgonzola, gruyere and other toppings.

In Philadelphia, the White Dog Café's grill menu features a grass-fed beef burger on a homemade bun, and now-legendary restaurateur Stephen Starr — of Buddakan fame — has Kobe sliders at his luxury steakhouse Barclay Prime.

In Chicago, Landmark Grill & Lounge has an appetizer of mini bison burgers on brioche with grilled pineapple, smoked bacon and barbecue sauce.

And aside from Tourondel's contributions to the craze in New York City, famed chef Daniel Boulud has a chi-chi sirloin burger stuffed with fois gras and black truffles at DB Bistro; Bobby Flay's "Burger Americain" at Bar Americain comes topped with Gruyere, cheddar, blue or goat cheese and the French restaurant Café D'Alsace offers a gourmet Alsatian-style burger flavored with Riesling wine, sweet onions and aioli and smothered in Muenster.

Even the fast-food chains are offering better burgers. Burger King and Carl's Jr. have hamburgers made with higher-grade Angus beef, and McDonald's own version is said to be in the works.

American consumers seem to be infatuated with the luxe burger, judging by how popular it's become as an upscale-restaurant menu item.

"I think it's great 'cause I'm a big fan of hamburgers," said Paul Friedman, 32, a lawyer in New York. "It's not like you're going to some disgusting burger joint — it's a nicer place and it doesn't seem so juvenile. I'm getting to the point in my life where a dive doesn't appeal to me anymore."

Mattson theorized that the upmarket twist on the burger could actually be a reaction to the foodie fad that's permeated the restaurant industry and American culture in recent years.

"In some ways, it's a backlash against the very fussy, froufrou, high-end food," she said. "There's nothing more comforting than a burger, nothing more familiar or safe."

Still, the upscale eats industry has seen about a 13 percent annual growth in recent years, according to the National Association for the Specialty Food Trade (NASFT), which sponsors the Fancy Food Show in several cities across the United States.

"If chefs are able to take what is traditionally considered the backyard dinner item to a higher level and stuff it with fois gras or top it with a rare mushroom, then they're seeing what we're seeing: Consumers are looking to buy higher quality foods," said Denise Shoukas, NASFT's communications director and a columnist for the association's Specialty Food Magazine.

That said, there can be a limit when it comes to prettying up the standard American fare that started as a simple beef patty on a white bread bun.

Tourondel doesn't think a truffle oil topping works, for instance. And in his view, a lobster burger is stretching it a bit, too.

"You have to come up with something a little bit different that's still tasty and not too fancy-fancy," he said. "You cannot put something very weird inside. It has to make sense."