Pulse the bacon and garlic in a food processor until coarsely ground.
Combine the ground pork, salt, pepper and sage in a large bowl. Add the bacon mixture and gently mix with your hands. Gently form the meat into 4 balls and then lightly press into 4" wide, 1" thick patties. Make a 2" wide indention in the center of each with your thumb to prevent the burgers from bulging when grilling.
Preheat grill to medium high. Season patties with pepper. Grill, undisturbed, until marked on the bottom, 5-6 minutes. Turn and grill other side until marked and patties feel firm, 4-6 more minutes. Meanwhile spread the cut sides of the buns with butter and toast on the grill.