In a small pot over medium high heat, melt the butter and add shallot and trimmings and fry a few minutes until it starts to brown. Add tomato, thyme and red wine and scrape out the solidified glace at the bottom of the pot with a wooden spatula. Cover, turn heat to low and let simmer for 1 hour. Strain, return to a clean pot and reduce by two thirds. Set aside.
In a large pot, bring water to a boil. Add a pinch of salt. Boil carrot and parsley root until just tender. Plunge into cold water, pat dry, drizzle with rapeseed oil, season with salt and pepper. Set aside. Rub the leg with salt and pepper. Place in a cooking bag and close tight. If you have a food saver, seal well.
Fill the kitchen sink with water measuring 140°F (60°C) – use a cooking thermometer.
Place the meat in the sink and let it sit for 3 hours. Check the temperature every 15 minutes or so, and make sure the temperature stays more or less stable, plus minus 10 degrees (5 C).
Remove from water, discard cooking bag and stick the cooking thermometer into the fattest part of the leg (making sure it’s not touching the bone). Transfer to a hot barbeque (or use the broiler in your oven) and grill on all sides until light golden brown. Meanwhile, grill the carrots and parsley roots.
Using a food brush, coat the meat with glaze. Continue to grill on all sides until crust is golden brown, the glaze has caramelized slightly and core temperature has reached 145°F (63°C).