2 frenched racks of lamb (1 1/2 lb each)
1/2 cup olive oil
1 1/2 tablespoons coarsely chopped fresh rosemary
1 large garlic clove, smashed

For berbere paste
1 tablespoon berbere
2 teaspoons Dijon mustard
2 teaspoons beaten egg yolk
1/4 cup fine bread crumbs made from day-old firm sandwich bread
1 to 2 tablespoons dry red wine

For sauce
2 tablespoons berbere
1/2 cup chicken stock or broth
1 tablespoon dry red wine
2 tablespoons cold unsalted butter, cut into pieces

Marinate lamb: Combine lamb, oil, rosemary, and garlic in a large sealable heavy-duty plastic bag. Seal bag, forcing out excess air, and marinate lamb, chilled, turning bag several times, 8 to 24 hours.

Preheat oven to 425 F.

Make paste and roast lamb: Stir together berbere, mustard, yolk, and bread crumbs, then stir in enough red wine to form a paste.

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.

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 140 F for medium-rare, 25 to 30 minutes.

Make sauce while lamb is roasting: Toast berbere in a dry small heavy saucepan over moderately low heat, stirring constantly, until very fragrant, about 1 minute. Add stock and wine and bring to a boil. Remove from heat and whisk in butter until incorporated.

Transfer lamb to a cutting board and let stand 5 minutes. Cut lamb into chops and serve with sauce.