Combine salt, pepper, thyme and rosemary and rub evenly over the lamb. Brown the meat on both sides in 30 ml of smoking hot olive oil.
Place the lamb on a rack and roast in a 2300 C oven for 13 minutes or until an internal temperature of 600 C is reached. Remove meat from oven and rest for 15 minutes.
Sautee the mushrooms in remaining olive oil until golden. Reduce the heat and add the artichokes and garlic. Sauté for 3 minutes. Sprinkle flour evenly over the top; mix in completely, forming a roux; cook for 5 minutes over low heat. Add beef stock, simmer for 10 minutes and season with salt and pepper. Keep warm.
Divide the mushroom mixture evenly among 4 plates. Slice the lamb rack and place 2 chops on top of vegetables. Spoon remaining sauce over the top of each portion.