Peel the garlic and cut it in little slices.
Cut a diamond pattern (each diamond should be about 1 inch long) into the fat side, using a sharp knife; this will produce a crispier crust. Rub the meat with salt, pepper, and garlic.
Heat the clarified butter in a large skillet and brown the meat on all sides. Place it fat side down in a roasting pan and pour the fat from the skillet plus the beer over it. Sprinkle it with caraway and rosemary. Arrange the onions around the meat.
Roast the meat for 1 hour and turn the fat side up. Increase the temperature and cook for another 30 to 45 minutes, basting frequently with beer. The meat is ready when the crust is browned and crunchy. Let the roast rest for 10 minutes before carving.
Deglaze the pan with the remaining beer and, if necessary, with 1/2 cup hot water or more. Strain the gravy into a small saucepan.
Simmer to thicken. Season with salt and pepper.
Cut the meat into thin slices and serve the gravy separately.