2 cups mirepoix (equal parts coarsely chopped onions, carrots and celery)
1/2 teaspoon whole black peppercorns
1 bay leaf
1 thyme sprig
to taste salt
1 tablespoon butter
1 tablespoon Dijon mustard
For the herbed crust:
1 cup fresh bread crumbs
1 teaspoon finely chopped thyme
3 tablespoons chopped parsley
2 large garlic cloves
Trim all but a thin layer of fat from the lamb. Cut off the last 2 inches of the rib bones.
Using a small sharp knife, scrape off any meat from the top 2 inches of each bone. Reserve all the trimmings.
Rub the racks with pepper and thyme sprig, then rub with a tablespoon olive oil.
Make lamb stock:
In a medium saucepan, brown the cut lamb bones and trimmings in remaining olive oil.
Add the mirepoix and brown for 2 to 3 minutes. Add the peppercorns, bay leaf and thyme. Add water to cover, bring it to a boil and simmer slowly until the stock is reduced to 1 cup.
Strain and reserve. Preheat the oven to 450 degrees.
Place the lamb in a shallow roasting pan. Season it with salt. Roast the rack for 10 to 12 minutes, or until the lamb is medium rare. Transfer the lamb to another pan.
While the lamb is resting, discard any grease from the roasting pan. Deglaze the pan with the lamb stock.
When the sauce has reduced slightly, whisk in 1 tablespoon of butter. Season the sauce to taste with salt and pepper and strain it. Keep the sauce warm.
Combine the herbed crust mixture in a food processor. Mix well until well blended. Brush the top side of racks with mustard. Spread herb mixture evenly over the mustard. Reduce oven temperature to 350 degrees. Place lamb in oven to brown crust. Transfer the racks to a serving platter. Separate the chops by cutting between the bones. -Letting the lamb rest after roasting distributes the juices evenly throughout the meat. Serve with ratatouille.