Adjust rack to middle position (middle and top positions for 4 servings) and preheat oven to 425 degrees. Wash and dry produce.

Trim and discard root ends and dark green tops from leeks. Halve lengthwise; rinse under cold water, gently separating inner layers to wash away any trapped grit. Pat dry with paper towels; thinly slice crosswise into half-moons. Peel and dice potatoes into ½-inch pieces. Trim and discard woody bottom ends from asparagus. Finely chop chives.

Heat 1 TBSP plain butter (2 TBSP for 4 servings) and a drizzle of oil in a medium pot over medium-high heat. Add leeks, a pinch of salt, and pepper. Cook, stirring occasionally, until softened and starting to brown, 2-4 minutes.

Stir in potatoes and add enough salted water to cover by 2 inches. Bring to a boil and cook until potatoes are tender, 15-20 minutes.

While leeks and potatoes cook, pat steak* dry with paper towels. Season all over with Steak Spice, salt, and pepper.

Heat a large drizzle of oil in a large pan over medium-high heat. Add steak and sear until browned all over, 3-4 minutes. Turn off heat; transfer steak to one side of a baking sheet (spread out across entire sheet for 4). Wipe out any burnt bits from pan.

On empty side of sheet, toss asparagus with a drizzle of oil, salt, and pepper. Roast on middle rack until asparagus is browned and tender and steak is cooked to desired doneness, 12-15 minutes. (For 4, toss asparagus on a second sheet; roast steak on top rack and asparagus on middle rack, swapping rack positions halfway through.) (For perfectly cooked steak, use a meat thermometer!)

Transfer steak to a cutting board to rest. (If steak is done first, carefully remove from oven and continue roasting asparagus.)

Once leeks and potatoes are done, reserve ¼ cup veggie cooking liquid (½ cup for 4 servings), then drain.

Carefully transfer veggies to a blender (or food processor). Add 1 TBSP plain butter, 2 TBSP crème fraîche, and 2 TBSP reserved veggie cooking liquid (2 TBSP butter, 4 TBSP crème fraîche, and ¼ cup reserved veggie cooking liquid for 4).

Blend, adding splashes of reserved veggie cooking liquid as needed, until no large pieces remain and mixture is smooth and creamy, 60-90 seconds. Season with salt and pepper to taste. TIP: To blend hot food safely, work in batches if needed, filling the blender only halfway. To blend, remove center cap from blender lid, secure lid on blender, and hold a folded kitchen towel over the lid to let steam escape and to protect yourself from splatters.

In pan used for steak, combine stock concentrate, mustard, and ¼ cup water (½ cup for 4). Bring to a boil, then remove from heat; whisk in remaining crème fraîche. Taste and season with salt and pepper if needed.

Transfer sauce to a small bowl; cover with foil until ready to serve. Wash and dry pan.

Pat scallops* dry with paper towels; season all over with salt and pepper.

Heat a large drizzle of oil in pan used for sauce over medium-high heat. Add scallops in a single layer; cook, undisturbed, until browned on one side, 3-5 minutes. Carefully flip; add garlic herb butter. Cook until opaque and cooked through, 3-5 minutes more.

Slice steak against the grain.

Divide steak, scallops and butter, potato-leek puree, and asparagus between plates in separate sections. Top puree with potato chips (crushing with your hands first) and spoon sauce over steak. Sprinkle chives over everything and serve.