Step 1

Preheat oven to 375 degrees F (190 degrees C).

Step 2

Season lamb generously with salt and black pepper. Heat oil over medium-high heat in an oven-proof skillet. Sear lamb on all sides until well browned, 3 to 5 minutes per side. Turn off heat. Remove lamb to a platter.

Step 3

Mix together Dijon mustard, rosemary, cinnamon, and cumin in a small bowl. Spread a thin layer of the mustard mixture on each rack of lamb.

Step 4

Place chopped shallots and pinch of salt into the same skillet. Cook and stir over medium-heat until shallots begin to lose moisture and become browned and soft, about 5 minutes. Add blueberries and continue cooking for about 2 minutes. Stir in red wine, turn off heat, and stir mixture to deglaze the pan.

Step 5

Place the racks of lamb into the skillet and interlace the rib bones together to push the lamb racks close together, leaving a lamb bone "zipper" in the center. Place the lamb racks into the center of the skillet. Season with a pinch of black pepper.

Step 6

Place skillet in pre-heated oven and roast lamb until internal temperature reaches 125 degrees F (52 degrees C) for medium-rare, about 20 minutes.

Step 7

Remove lamb to a cutting board to rest about 5 minutes.

Step 8

Drizzle balsamic vinegar into the blueberry sauce; add a pinch of salt. Turn heat to medium-high and bring to a simmer to reduce sauce by half, about 4 minutes. Turn off heat and stir in butter. When butter is melted, check seasonings and add more salt if needed.

Step 9

Slice racks into pieces of 2 ribs each. Serve topped with a spoonful of the blueberry sauce.