Adjust rack to top position and preheat oven to 425 degrees. Wash and dry all produce. Cut broccoli florets into bite-size pieces, if necessary. Dice potatoes into 1/2-inch pieces. Peel and mince or grate ginger.

Toss broccoli on a baking sheet with a large drizzle of olive oil, salt, and pepper. Roast on top rack until tender and browned at edges, 15-20 minutes. Meanwhile, place potatoes in a medium pot with enough salted water to cover by 2 inches. Boil until tender, 15-20 minutes.

While potatoes cook, place sesame seeds in a large, dry pan over mediumhigh heat. Cook, stirring often, until golden brown and toasted, 1-2 minutes. Turn off heat; transfer to a small bowl. Wipe out pan.

Once potatoes are tender, reserve 1/2 cup potato cooking liquid, then drain and return potatoes to pot. Add sour cream, 1 TBSP butter (2 TBSP for 4 servings), and wasabi paste to taste. Mash until smooth, adding splashes of reserved potato cooking liquid as needed. Season with salt and pepper. Cover to keep warm.

Pat steak dry with paper towels. Season generously all over with salt and pepper. Heat a large drizzle of oil in pan used for sesame seeds over mediumhigh heat. Add steak and cook to desired doneness, 3-6 minutes per side. Turn off heat; transfer to a cutting board to rest. TIP: If there’s excess grease in your pan, carefully pour it out.

Heat same pan over medium heat. Add 1 TBSP butter (2 TBSP for 4) and as much ginger as you like. Cook, stirring, until fragrant, 1-2 minutes. Stir in any resting juices from steak. Add teriyaki sauce; bring to a simmer. Turn off heat. Season with salt and pepper. Divide potatoes and broccoli between plates. Slice steak against the grain; arrange over potatoes. Spoon sauce over steak. Top with as many sesame seeds as you like.