Lamb roast with Caramelized potatoes

I find that cooking meat using internal temperature much more satisfying. We bought a boneless lamb leg roast at the farmer's market on Comox street and I had to figure out what to do with it. Here's what I came up with.

5 lb. leg of lamb/lamb shoulder, boneless

3 garlic cloves, peeled and sliced

1 tsp. salt and pepper

2 Tbsps. lemon juice

1/4 cup olive oil, plus a little more for the potatoes

Several handfuls of herbes de Provence

2 lbs. potatoes, sliced about the width of your little finger

1/2 cup veal or beef stock

1. Several hours before cooking the lamb, make slits all over it with the tip of a sharp knife and slide a sliver of garlic into each slit as you go. Stir together the salt, pepper, lemon juice, and olive oil. Now, pat the herbs all over the meat to cover completely. Cover and leave to marinate for several hours in the refrigerator (I wrap it up again in the brown paper the roast came in). Let come to room temperature an hour before roasting.
2. Heat the oven to 450ºF with the top cooking rack mid-way, and another rack beneath it two notches down. Toss the potatoes on a baking sheet (with sides) or roasting pan with a little olive oil, and season with salt and pepper. Pour over the stock. Put the potatoes on the lower oven rack and the lamb roast directly on the rack above it, so that drippings will fall through directly onto the potatoes. During cooking, pour a little more stock or water in on the potatoes if they look dry at half-time. They are done when they are soft and nicely caramelized, glossy and sticky.
3. FOR BONELESS SHOULDER: Roast the lamb 20 minutes, then lower the heat to 400ºF and continue roasting (Laura says 40 minutes but for the boneless shoulder roast, this is too much. Take temperature reading after 20 minutes to work out the correct time) before checking with a meat thermometer - 140F for rare, 155F medium, 165F well done (temperature will rise about 5 degrees out of oven).
4. FOR BONE-IN LEG: Preheat oven at 450°F. Roast the leg for 20 minutes and then lower heat to 325°F for the rest of the cooking time of 2 hours (CHECK after 60 minutes, then every 20 minutes). The roast is done when an instant read thermometer inserted into thickest part of leg reads at least 140°F (for rare, see chart link, above) (temperature will rise about 5 degrees out of oven).
5. Rest the meat 10 minutes before carving. The meat will continue to cook, the internal temperature rising even more during this time, and at the same time the juices will flow back to the edges of the meat. Serve with the potatoes.