Bring 3 TBSP butter (6 TBSP for 4 servings) to room temperature. Wash and dry all produce. Peel and dice sweet potatoes into ½-inch pieces. Place in a medium pot with enough salted water to cover by 2 inches. Bring to a boil and cook until tender, 15-20 minutes. Drain and return sweet potatoes to pot.

Meanwhile, thinly slice chives. Trim and discard woody bottom ends from asparagus. Put peppercorns in a zip-close bag and crush with a heavy-bottomed pan or rolling pin; pour onto a plate and spread into an even layer. Pat beef dry with paper towels; season all over with salt. Press both sides of beef into peppercorns to evenly coat. TIP: For a milder flavor, sprinkle beef with peppercorns instead.

Heat a drizzle of oil in a large pan over medium-high heat. Add beef and cook almost to desired doneness, 4-7 minutes per side. Add stock concentrate and 2 TBSP water (3 TBSP for 4 servings). Simmer until sauce has thickened and beef reaches desired doneness, 1-2 minutes more. Turn beef to coat, then transfer everything to a shallow dish. Turn off heat; wipe out pan.

Heat a drizzle of oil in same pan over medium-high heat. Add asparagus; season with salt and pepper. Cook, stirring, until lightly browned and tender, 3-5 minutes. Transfer to a plate. Add almonds to same pan; cook, stirring, until lightly toasted, 1 minute. Season with salt and pepper. Transfer to a small bowl.

Mash sweet potatoes until smooth. (TIP: If potatoes have cooled, mash over medium-low heat.) Stir in sour cream and 1 TBSP softened butter (2 TBSP for 4 servings) until combined. Season generously with salt and pepper.

In a second small microwave-safe bowl, combine remaining 2 TBSP softened butter (4 TBSP for 4 servings), 1 tsp chives (2 tsp for 4), salt, and pepper. (TIP: If butter is still cold, microwave 5-10 seconds.) Divide beef, sweet potatoes, and asparagus between plates. Sprinkle asparagus with almonds. Top beef with chive butter. Garnish with remaining chives and serve.