Place brisket in large Dutch oven. Sprinkle with sugar and cloves; then pour ale and 1-1/2 cups water into pot.
Simmer covered over low heat, turning brisket twice, until beef is fork-tender, about 2-1/2 hours. Add carrots and parsnips after 1 hour's cooking time.
Remove beef from Dutch oven and keep warm. Cut carrots and parsnips lengthwise into quartrs and toss with butter and parsley. Keep warm.
Skim fat from pan juices. Measure 2 cups juices. Mix cornstarch, 1 t. water, the vinegar, and salt. Whisk pan juices and cornstarch mixture in small saucepan. Heat to boiling, stirring constantly, and boil 1 minute. Pour gravy into sauceboat.
Slice meat and arrange with carrots and parsnips on large serving platter.