I would skip the routabaga, personally they can give off a bitterness. I would opt for fresh rosemary too.
Bone in or boneless? I prefer boneless stuff a bunch of whole garlic in the cavity and truss up the leg brown then slip in fresh rosemary twigs.
Mirepoix rack, hearty red wine and let it roast uncovered. Add veggies about midway. Until about 125-130*f pull it off the rack and let it sit, wrap in foil if you want. Drain juices into sauce pan, deglaze the and scrape the pan with red wine, dump in sauce pan with juices. Bring up to a simmer, skim, tighten with
burre manie finish with mint jelly to taste. Fresh mint will leave a vegetal flavor so don't use it other than for garnish. The jelly will impart a nice mint background to the sauce which will be very complementary.