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1
Preheat oven to 350u00b0.
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2
Remove white papery skin from garlic heads (do not peel or separate the cloves). Cut off top portions of garlic heads. Wrap garlic heads in foil. Bake at 350u00b0 1 hour; cool 10 minutes. Squeeze garlic heads to extract pulp. Discard skins. Place garlic pulp, mustard, and oil in a food processor; process until smooth. Stir in chives and thyme leaves.
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3
Increase oven temperature to 425u00b0.
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4
Trim fat from lamb. Cut 12 3/4-inch slits in lamb; place a fresh garlic slice in each slit. Sprinkle surface of lamb with 1/2 teaspoon salt and pepper; rub with roasted garlic paste mixture. Press breadcrumbs over surface of lamb. Place lamb on a broiler pan. Insert meat thermometer into thickest part of lamb, making sure not to touch bone.
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5
Bake at 425u00b0 for 10 minutes. Decrease oven temperature to 325u00b0. Bake an additional 2 hours and 10 minutes or until thermometer registers 140u00b0 (medium-rare) to 155u00b0 (medium). Remove lamb from rack; place on a shallow serving platter. Lightly cover with foil; let stand 15 minutes.
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6
Drain fat from bottom of pan (do not scrape pan). Place broiler pan on stovetop over medium-high heat. Add broth, and bring to a boil, scraping to loosen browned bits.
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7
Combine red wine and cornstarch, and stir with a whisk. Add to beef broth, and return to boiling. Cook 1 minute or until mixture is slightly thick, stirring constantly. Stir in 3/4 teaspoon salt, and serve immediately with lamb. Garnish with thyme sprigs, if desired.
