To make the pesto, in the bowl of a food processor, combine the parsley, mint, garlic and olive oil and process until smooth. Add the Parmigiano-Reggiano cheese, pine nuts and salt and process until all the ingredients are combined. Set aside.
To make the lamb burgers, prepare a charcoal or gas grill for grilling over medium heat. Line a baking sheet with plastic wrap.
Divide the blue cheese evenly into 6 pieces and shape each piece into a 2-inch disk. Set aside.
In a bowl, combine the lamb, parsley, rosemary, salt and pepper. Do not overmix. Divide the lamb into 6 portions. Mold each portion around a piece of cheese and shape into a rough ball, then flatten slightly into a 4-inch-diameter patty, making sure the cheese is completely encased within the lamb. Place the patties on the prepared tray, cover and refrigerate until ready to cook.
Grill the burgers, turning once, until the cheese is melted and the meat is mediumrare, 4 to 5 minutes per side. Serve the burgers with the pesto.
Adapted from Williams-Sonoma TASTE Magazine, “Lunch on the Porch,” by Donata Maggipinto (Summer 2002).