Blend all the marinade ingredients in a bowl. Put the lamb leg into a shallow bowl or a turkey-roasting bag, and add the marinade. Refrigerate overnight.
About three hours before you're planning to serve dinner, preheat the oven to 475 degrees.
Remove the lamb leg from the marinade and shake off the excess. Place the lamb on a cutting board and trim off excess fat. Then season it all over with the Creole seasoning and the salt. Place it with the meatier side down on a rack inside a pan. Pour the marinade into the pan.
Put the lamb leg onto the lowest shelf in the oven and and turn the temperature down to 350 degrees. Roast it for a half-hour. Turn the leg and spoon some of the pan liquids over it. Check it every 10 or 15 minutes, and baste the leg with the juices again. Add more water if the juices in the pan begin to dry out.
The lamb is done to medium-rare when a meat thermometer inserted in the center (but not touching the bone) reads 125-130 degrees. (For medium, go to 140 degrees.)
Wrap the leg with aluminum foil and allow to cool in a pan on the counter for 20-25 minutes. Meanwhile, pour all the juices from the roasting pan into a separator. When it settles, pour the defatted juices into a saucepan. Bring to a boil and reduce to about a cup. Add salt and pepper to taste.
To slice the lamb, make vertical cuts from the meatier side of the leg straight down as if going through the bone. Then cut across the lowest parts of the vertical cuts to free the slices. Repeat this process all the way around. It's best not to slice the lamb parallel to the bone, because that's the way the grain runs.
