Chris Kimball's old-fashioned burger with classic sauce is seen in this May 2, 2010 photo. Using coarsely ground sirloin steak and boneless beef short ribs makes this burger a winner. (AP Photo/Larry Crowe) (Larry Crowe)
10 ounces sirloin steak tips , cut into 1-inch chunks
6 ounces boneless beef short ribs, cut into 1-inch chunks
1 tablespoon unsalted butter, divided
4 soft hamburger buns
1/2 teaspoon vegetable oil
4 slices American cheese
Thinly sliced onion
To prepare the classic sauce, in a small bowl whisk together the mayonnaise, ketchup, relish, sugar, vinegar and black pepper. Set aside.
To prepare the burgers, place the steak and rib chunks on a baking sheet in a single layer, leaving 1/2 inch of space around each chunk. Freeze the meat until very firm and starting to harden around edges but still pliable, 15 to 25 minutes.
Place half of the meat in a food processor and pulse until it is coarsely ground, 10 to 15 quick pulses, stopping and redistributing the meat around bowl as necessary to ensure the beef is evenly ground. Transfer the meat to the baking sheet, overturning the bowl and without directly touching meat. Repeat grinding with remaining meat.
Spread the meat over sheet and inspect carefully, discarding any long strands of gristle or large chunks of hard meat or fat.
Gently separate the ground meat into 4 equal mounds. Without picking up the meat, use your fingers to gently shape each mound into a loose patty 1/2 inch thick and 4 inches in diameter, leaving the edges and surface ragged. Season the top of each patty with salt and pepper. Using a spatula, flip the patties and season the other side. Refrigerate.
In a heavy-bottomed 12-inch skillet over medium, melt 1/2 tablespoon of the butter until foaming. Add the bun tops, cut-side down, and toast until light golden brown, about 2 minutes. Repeat with remaining butter and bun bottoms. Set buns aside and wipe out the skillet with paper towels.
Return the skillet to high heat. Add the oil and heat until just smoking. Using a spatula, transfer the burgers to the skillet and cook without moving for 3 minutes. Flip the burgers over and cook for 1 minute. Top each patty with a slice of cheese and continue to cook until the cheese is melted, about 1 minute longer.
Transfer the patties to the bun bottoms and top with onion. Spread 2 teaspoons of burger sauce on each bun top. Cover burgers and serve immediately.