Set up an ice bath with cold water in a large bowl.
Bring a few inches of water to a boil. Add salt then cook asparagus 2 minutes; cold-shock and dry. Add scallions to boiling water and blanch 45 seconds to 1 minute; cold-shock and dry.
Arrange the meat on parchment or plastic in a single layer with a bit of space between each slice. Top with plastic or parchment and gently pound to 1/16-inch thick; season with pepper.
Working on cutting board, shingle/layer 3 or 4 slices of meat to form a 7- to 8-inch square. Place 3 scallions and 3 asparagus on each square and roll them up in the meat; secure each roll with 2 or 3 pieces of kitchen string. Repeat to form 3 more rolls.
Combine sake, Mirin, Tamari, ginger and garlic in a shallow dish. Add beef rolls and marinade 15 minutes, turning them occasionally to coat all over with sauce.
While meat marinates, stem spinach and arrange on a platter or individual dishes. Arrange radish matchsticks, carrots and red peppers over the spinach.
Place the dressing ingredients in a blender and blend until smooth. Adjust salt and pepper, and reserve.
Heat a large, cast-iron skillet over medium-high heat with oil, 1 turn of the pan. Shake off any excess marinade and add rolls to skillet. Cook 5-6 minutes for medium-rare center and crispy outer layer; remove to cutting board. Add marinade to pan and reduce 1-2 minutes to form a syrupy sauce.
Cut string off beef rolls and cut each roll into 5 pieces, arrange pinwheels upright on plates in a small pool of the reduced sauce.
Spoon dressing over salad and serve alongside the negimaki. MORE
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