Adjust rack to upper position and preheat oven to 425 degrees. Wash and dry all produce. Halve, peel, and thinly slice shallot. Trim woody bottom ends from asparagus. Peel sweet potatoes, then dice into 1/2-inch pieces. Crush peppercorns in a zip-close bag with a rolling pin or a heavy pan.

Place sweet potatoes in a medium pot with enough salted water to cover by 2 inches. Cover, bring to a boil, and cook until tender, about 10 minutes. Meanwhile, melt 1 TBSP butter (2 TBSP for 4 servings) in a large pan over medium-high heat. Add shallot and a pinch of salt and sugar; cook until browned, 5-8 minutes. TIP: If shallot browns too quickly, add 1 TBSP water to pan.

Transfer shallot to a small bowl. Pat steak dry with paper towels and season all over with salt. Press 2 tsp crushed peppercorns (1 TBSP for 4 servings) into steak to form a crust. (TIP: For a milder flavor, sprinkle steak with peppercorns instead.) Heat a large drizzle of olive oil in pan used for shallot over mediumhigh heat. Add steak and cook to desired doneness, 3-6 minutes per side. Transfer to a plate. Wash and dry pan.

Meanwhile, toss asparagus with a large drizzle of olive oil on a baking sheet. Season with salt and pepper. Roast until just tender, 7-10 minutes. Drain sweet potatoes and return to pot. Mash with sour cream and 1 TBSP butter (2 TBSP for 4 servings). Season with salt and pepper. Cover to keep warm.

Heat same pan over medium heat. Return shallot to pan along with a pinch of remaining crushed peppercorns. Stir in stock concentrate and 1/4 cup water (1/3 cup for 4 servings). Simmer until slightly thickened, 2-3 minutes. Turn off heat. Stir in 1 TBSP butter (2 TBSP for 4 servings) and any resting juices from steak.

Slice steak against the grain. Divide between plates and spoon sauce on top. Serve with mashed sweet potatoes and roasted asparagus alongside.