Preheat oven to 350°.
Tie the roast at 2-inch intervals with twine; rub with salt and pepper. Heat oil in Dutch oven over medium-high heat. Add roast; cook 12 minutes, browning on all sides. Remove roast from pan. Add onion and water to pan, scraping pan to loosen browned bits. Return meat to pan.
Place rosemary, thyme, sage, and bay leaves on a double layer of cheesecloth. Gather edges of cheesecloth together; tie securely. Add cheesecloth to pan; cover, reduce heat, and simmer. Bake, covered, at 350° for 1 1/2 hours. Turn roast; bake, covered, an additional 45 minutes. Add carrots and dried plums; bake, covered, an additional 45 minutes or until carrots are tender.
Place roast, carrots, and dried plums on platter; keep warm. Reserve cooking liquid. Discard bag.
Place a zip-top plastic bag inside a 2-cup glass measure. Pour reserved cooking liquid into bag; let stand 2 minutes (fat will rise to the top). Seal bag; carefully snip off 1 bottom corner of bag. Drain drippings into measuring cup, stopping before fat layer reaches opening; discard fat. Slice roast; garnish with sage leaves, if desired. Serve with carrot mixture and sauce.