Hubert Keller, chef-owner of San Francisco– and Las Vegas–based restaurant Fleur de Lys and a television mainstay (Secrets of a Chef, Top Chef, Top Chef Masters), is obsessed with hamburgers, as any self-respecting Frenchman should be. Here he generously shares some of his secrets. (More can be found in his book Burger Bar: Build Your Own Ultimate Burgers.)
Slowly softening the onion and garlic is key to a silky, creamy blended sauce. If you have Madras curry powder, use it for slightly more heat and richer flavor; standard curry powder will also be great.