You can upscale a burger too far. That $120 DB Royale black truffle burger? It's all about the illusion of luxury. Four-week-aged-beef burgers, Kobe burgers, burgers larded with foie gras — meh. Chef Deepak Kaul does the bistro burger just right, with straightforward panache: a fat round of Prather Ranch beef, an Acme roll, a tangle of pink pickled onions, and a few precise leaves of lettuce. Kaul serves a mellow blend of Dijon and whole-grain mustard on the side, as well as several slices of housemade bread-and-butter pickles. Straightforward, right? But the thing that makes Serpentine's burger so good is its obscene juiciness. We've bitten in and watched pink juices spurt out all over the plate, felt them run down our chin, felt our mouths fill with fat and flavor. It's an impressive effect, all the more because Kaul didn't resort to gimmicks to achieve it.