- With the rack in the middle position, preheat the oven to 140 °C (275 °F).
- In a skillet, brown the roast on all sides in the oil and half the butter. Season with salt and pepper. Remove the meat from the pan. Set aside.
- In the same skillet, sauté the onions in the remaining butter. Add the garlic, wine and herbs. Season with salt and pepper.
- Pour the content of the skillet in a roasting pan. Place a wire rack in the pan and top with the roast. Insert a meat thermometer in the centre of the piece of meat. For rare meat, cook for about 1 hour and 55 minutes or until the thermometer reads 55 °C (130 °F).
- Remove the roast from the oven. Cover with aluminum foil. Let stand for 15 minutes. The internal temperature should rise to 60 °C (140 °F).
- Before serving, thinly slice the roast. Serve with the onion sauce and mashed potatoes.