9 cups small, tender greens, such as baby arugula or Bibb lettuce
Active time: 40 minutes
Total time: 1 hour, 40 minutes
Note: Feel free to substitute any root vegetables for the carrots and radishes.
Season steak all over with 1/2 tsp. salt and pepper; cover loosely and set aside at room temperature for 1 hour.
Meanwhile, bring a large pot of salted water to a boil. Add carrots and leeks, cook for 1 minute, drain well, and transfer to a large plate; set aside. In a medium bowl, combine mayonnaise, miso, 1/2 tsp. lemon juice, mustard, sugar, and cayenne pepper; set aside. In a medium bowl, toss sugar snap peas and radishes with 1/2 tsp. salt; set aside.
Heat 1 Tbsp. oil in a large skillet over medium-high heat. Add steak and cook, flipping halfway and being sure to brown the sides, until rare to medium-rare, 8 to 10 minutes. Transfer to a plate, let rest for 5 minutes, and then thinly slice against the grain.
In a large bowl, whisk together remaining 2 Tbsp. oil, 1 Tbsp. plus 1 tsp. lemon juice and 1/4 tsp. salt, then add greens and toss well. Drain radishes and sugar snap peas of any accumulated water. Divide miso mustard among 6 plates. Top with beef, carrots, leeks, sugar snap peas, radishes, and greens and serve.