Ever since Daniel Boulud started stuffing hamburgers with foie gras and short ribs (and low-fat lost the PR battle to low-carb), chefs have been rethinking that franchise favorite as a serious menu investment. Foie gras, upscale fungi, famous-name onions -- the sky, or the expense account, is the limit. For example:

CHARLIE PALMER STEAK -- 101 Constitution Ave. NW; 202-547-8100. Fourteen-ounce Angus burger with fois gras, oil-cured tomatoes and choice of Vermont Grafton Cheddar or Berkshire Blue cheeses on house-made brioche, $23. Three mini-burgers with foie gras, stone-ground mustard and baby romaine, $10.

CITRONELLE -- 3000 M St. NW in the Latham Hotel; 202-625-2150. "Lobster burger" of a quarter-pound lobster-scallop mousse, tomato confit, mache and ginger-soy mayonnaise on house-made bun, $20.

FAIRMONT LOBBY LOUNGE -- 24th and M streets NW in the Fairmont Hotel; 202-429-2400. Three mini-"sliders" of Kobe beef with truffle-foie gras-Vidalia onion relish on house-made brioche, $10.

INTERNATIONAL BAR -- 10 Thomas Cir. NW in the Washington Plaza Hotel; 202-842-1300. Half-pound Black Angus burger with seared foie gras, chanterelles, caramelized Vidalias and Gruyere cheese, $16.

SAVEUR -- 2218 Wisconsin Ave. NW; 202-333-5885. "Bacon cheeseburger," pictured at left, of nine ounces Black Angus beef stuffed with Camembert cheese and wrapped in prosciutto on brioche bun, $9.

SIGNATURES -- 801 Pennsylvania Ave. NW; 202-628-5900. "Steak and Cheese" of eight ounces shaved Kobe beef, sauteed onions and peppers and Provolone and Swiss cheeses on toasted baguette, $16.

-- Eve Zibart