Remove any loose papery skin from garlic,leaving heads intact.In a large roasting pan,place roast,fat side up,and garlic.Insert a meat thermometer into center of roast,being careful that the point does not touch the bone. Roast beef in a 325 degree oven until thermometer reaches 140 degrees for rare,23 to 25 minutes per pound or until of desired doneness. Meanwhile,cut each onion,lengthwise,in half.Peel carrots and parsnips;cut each lengthwise in half,if large.After roast has roasted 1 hour,remove garlic and cool until easy to handle.After beef has roasted 1 1/2 hours,add onions to drippings in roasting pan,turning to coat with drippings.Roast 45 minutes,turning onions occasionally,until fork tender.While beef and onions are roasting,press soft,cooked garlic from each clove into a bowl.Stir in parsley and black pepper;set aside. In a 12" skillet over high heat,heat 3/4" water and carrots to boiling.Reduce heat to low;cover and simmer about 15 minutes or until tender.Drain;add minced tarragon,1 tablespoon butter and 1/4 teaspoon salt.Keep warm.In a 10" skillet over high heat,cook 3/4" water and parsnips to boiling.Reduce heat to low;cover and simmer about 15 minutes or until tender.Drain parsnips;remove to plate.In the same skillet over medium heat,cook 2 tablespoons butter and 1/4 teaspoon salt until butter turns golden brown,stirring.Return parsnips to skillet,turning them to coat with butter.Keep warm. When onions are done,remove to a bowl;keep warm.Evenly,spread garlic paste mixture over beef.Roast about 30 minutes longer or until coating is golden and beef is of desired doneness. When beef is done,place on a warm large platter with carrots,parsnips and onions.Keep warm while preparing red wine au jus gravy.Skim any fat from meat drippings;add red wine,bouillon and 1 1/4 cups water.Over medium heat,heat mixture to boiling,stirring constantly and scraping until brown bits are loosened from bottom of pan.Serve beef roast with red wine au jus.