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 60ºC or 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 1.5 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 30 cm skillet over high heat,heat 2 cm 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 quarter teaspoon salt.Keep warm.In a 25 cm skillet over high heat,cook 2 cm 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 quarter 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 1.25 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.