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Stir together berbere, mustard, yolk, and bread crumbs, then stir in enough red wine to form a paste.
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Drain lamb, discarding marinade. Heat a dry 12-inch heavy skillet over high heat until hot, then brown lamb, 1 rack at a time, over moderately high heat, about 3 minutes per side (do not brown ends). Transfer, ribs side down, as browned to a large roasting pan.
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Smear berbere paste on fat sides of lamb and roast in middle of oven until an instant-read thermometer inserted 2 inches into center of a rack (without touching bone) registers 140ºF for medium-rare, 25 to 30 minutes.