Bone and tie the beef roast. Cut slits into the roast and insert the slivered garlic, placing the pieces evenly around the roast. Rub the roast with 1 tablespoon of the mustard, and sprinkle it with the thyme.
Place the roast on a roasting rack. Top the roast with the bacon, with the ends covering the sides. Insert a meat thermometer into the thickest portion of the meat and roast at 325 degrees F until the thermometer registers 145 degrees F for rare, or 160 degrees F for medium to well-done.
Transfer the meat to a serving board or platter. Remove the bacon and string, then replace the bacon. Pour the pan drippings into a small skillet and whisk in the remaining mustard. Heat to boiling. Continue boiling until the drippings are shiny and thickened. Spoon the sauce over the roast and slice it. Serve immediately.