Place the ground beef in a medium bowl and sprinkle liberally with salt and pepper. Using your hands, gently mix the seasonings with the meat. Brush a baking sheet with oil or spray with cooking spray. Using a 2-inch biscuit cutter as your form, make 12 mini burgers. Make sure that you put a thumbprint indention in the center of each one. Cover with plastic wrap and refrigerate for about 1 hour.
Meanwhile, combine the butter, shallots, Worcestershire, and granulated onion in a small bowl. Season with salt and pepper. Refrigerate if it’s going to be longer than an hour before you grill, but you want this butter to be soft and at room temperature when using.
Oil the grill racks. Preheat your grill using all burners set on high and with the lid closed for 10 to 12 minutes.
Split your party rolls in half and put them, cut side down, on the grill. Toast for about 2 minutes. As you take them off, smear them with the butter on the insides. Place on a platter and tent with foil. Place the burgers on the grill and grill for about 3 minutes. Turn and continue grilling for an additional 2 to 3 minutes. Remove to a platter. Add one burger to each roll and serve with your favorite condiments.