2 1/4 # ground beef chuck, 80% lean
6 oz strongly flavored blue cheese
6 burger buns
1/2 stick butter, melted
1 head radicchio, leaves separated
1 small red onion, thinly sliced
2 large ripe tomatoes, thickly sliced
vegetable oil, for grilling
kosher salt & freshly ground black pepper, to taste
Preheat the grill to very hot, about 30 minutes. Here’s a way to tell if your grill is at the right temperature. Hold your hand right over it. If you you can keep it there for five seconds, it’s not hot enough. If you can’t hold it there for even half a second, it's too hot. When the grill is hot, scrape it clean with a metal brush. Soak a rag or a bunch of paper towels with a few tablespoons of vegetable oil, and using tongs, rub it over the grill rack.
Gently shape the ground beef into six 6-ounce patties, being careful not to over-work the meat (or the burgers will turn out less tender). Slice the buns in half, then brush the insides evenly with melted butter.
Just before grilling, generously season both sides of each patty with salt and pepper.
Arrange the burgers over the hottest area of the grill, over direct heat. Grill, uncovered, without pressing down on the patties (For some reason, people always want to do this. They think it speeds up the cooking time. But all it accomplishes is to squeeze out precious juice). Cook until well seared on the first side, about 2 1/2 minutes. Flip the burgers over with a metal spatula, top each with about an ounce of blue cheese, then continue cooking - about 2 minutes for rare, 2 1/2 minutes for medium-rare, 3 minutes for medium, 4 minutes for medium-well and about 4 minutes on each side for well done. Remove the burgers, then toast the buns on the grill, cut side down, until lightly browned, about a minute.
On top of each bottom bun place two large radicchio leaves. The set the burger, cheese side up, on top of the radicchio. Top the burger with the sliced onions, then the tomato slices. Sprinkles with a bit of salt. Top everything with the top bun. Serve immediately.