Preparation

Make the crumb coating

• Pulse the bread cubes, pine nuts, Parmigiano-Reggiano, lemon zest, garlic, 1/2 tsp. salt, and 1/2 tsp. pepper in a food processor until coarse crumbs form. Transfer to a medium bowl.

Make the pesto

• Pulse the parsley, rosemary, oil, lemon zest, garlic, and 1/2 tsp. salt in the food processor until a coarse paste forms.

Sear the lamb

• Heat a heavy-duty 12-inch skillet over medium-high heat until hot. Rub the lamb racks all over with the oil and then, working with one rack at a time, sear them, meat side down, until browned, about 4 minutes each. Pour off any accumulated fat, as necessary. Let rest on a cutting board for about 20 minutes to cool.
• Meanwhile, position a rack in the center of the oven and heat the oven to 375°F.

Roast the racks

• Rub one-third of the pesto over the meat side of each rack. Firmly press the crumb coating over the pesto. Arrange the racks bone side down in a large roasting pan (if the racks seem crowded, rest the bones on the edge of the pan). Roast until the crumbs are browned and a probe or instant-read thermometer inserted into the eye of the meat registers 135°F for medium rare, 25 to 30 minutes, or 145°F for medium, about 40 minutes.
• Let the racks rest in the pan at room temperature for 10 to 15 minutes. Transfer to a carving board and carefully slice between the bones to make individual chops. Lightly sprinkle the cut sides of each chop with sea salt and serve with any crumb coating that fell off during carving.

Make Ahead Tips

You can make both the crumb coating and pesto up to 1 day ahead and keep them refrigerated in separate airtight containers.