MUSHROOM AND SWISS CHEESE BURGERS (Pennsylvania, for four)
1-½ pounds 100% ground chuck (about 80% lean)
1 teaspoon salt
½ teaspoon ground black pepper
vegetable oil for grill rack
4 hamburger buns
10 ounces thinly sliced mushrooms (about 4 cups)
2 tablespoons unsalted butter
4 slices Swiss cheese
grainy mustard to taste (optional)
1. Break up chuck to increase surface area for seasoning. Sprinkle salt and pepper over meat and toss lightly with hands to distribute. Divide meat into 4 equal portions (6 ounces each). With cupped hands, toss one portion back and forth to form a loose ball. Pat lightly to flatten meat into a ¾ inch thick burger that measures about 4-1/2 inches across. (Do not over-handle meat or your burger will be tough). Pressing down with your thumb, or with the back of a measuring spoon, make a ¼ inch depression in the center of each patty, creating a shallow well. (This makes them come out flat, not puffed in the center). Repeat with remaining portions of meat.
2. Melt butter in a medium skillet and saute the mushrooms over medium heat until they are tender, about 5 minutes.
3. Heat a well-seasoned large cast-iron skillet over moderately high heat until it is hot, sprinkle it evenly with coarse salt, and when the skillet is hot enough that the salt begins to color slightly, add the patties. For medium rare burgers, cook for 4 minutes on one side, flip the burgers over and cook for 4 minutes on the other side. Sprinkle them with the sauteed mushrooms, top each burger with a slice of cheese, cover and cook until the cheese melts. Spread buns with mustard, add burgers and serve immediately.