Season the racks of lamb with salt and pepper. Let stand at room temperature for 1 hour. In a bowl, stir together the bread crumbs, rosemary, salt and pepper. In a small bowl mix the mustard, egg and garlic.
Preheat an oven to 375°F.
Brush the meaty side of each lamb rack with 1 Tbs. mustard mixture.
Pack the bread crumb mixture onto the meaty side.
In a large fry pan over medium-high heat, warm the olive oil until just smoking. Add the lamb racks, bread-crumb side down, and brown on both sides, about 2 minutes per side. (you can prepare the lamb up to a day ahead of time and stop here, then finish 40 minutes before you're ready to eat.)
Bake in the oven for 20 to 25 minutes.
Transfer the lamb to a carving board, cover loosely with aluminum foil and let rest for 15 minutes. Carve the racks into double chops and serve immediately. Place the racks, bread-crumb side up, on a rack in a roasting pan. Transfer to the oven and roast until the crust is nicely browned and an instant-read thermometer inserted into the thickest part of the meat, away from the bone, registers 130°F for medium-rare, 20 to 25 minutes, or until done to your liking.
When placing the racks in the roasting pan, set them so the bones are crossed at the top.