Adjust rack to middle position (top and middle positions for 4 servings) and preheat oven to 450 degrees. Wash and dry produce.

Halve potatoes lengthwise. Strip rosemary leaves from stems; finely chop leaves until you have ¼ tsp (½ tsp for 4). (We sent more; save the rest for another use!) Halve, peel, and thinly slice onion. Zest and quarter lemon. Trim and discard woody bottom ends from asparagus.

Toss potatoes on one side of a baking sheet with a drizzle of oil, chopped rosemary, salt, and pepper.

Roast on middle rack for 14 minutes (you’ll add the asparagus then). (For 4 servings, spread potatoes out across entire sheet.)

Meanwhile, heat a drizzle of oil in a medium, preferably nonstick, pan (use a large, preferably nonstick, pan for 4 servings) over medium-high heat. Add onion and ¼ tsp thyme (½ tsp for 4); cook, stirring occasionally, until browned and softened, 5-8 minutes.

Stir in stock concentrate, ¼ cup water, 1 tsp sugar, and 1 tsp lemon juice (for 4, use ½ cup water, 2 tsp sugar, and 2 tsp lemon juice). Cook until thickened and saucy, 2-3 minutes more.

Remove from heat; stir in 1 TBSP butter (2 TBSP for 4) until melted. Taste and season with salt and pepper if desired. Transfer to a medium microwave-safe bowl; tightly cover with plastic wrap. Rinse and wipe out pan.

While onion cooks, in a second medium bowl, combine sour cream, horseradish sauce, mayonnaise, and a squeeze of lemon juice. Season with salt and pepper to taste.

Pat steak* dry with paper towels and season generously all over with garlic powder, ½ tsp dried thyme (1 tsp for 4 servings), salt, and pepper. (Be sure to measure the thyme—we sent more!)

Once potatoes have roasted 14 minutes, remove sheet from oven. Carefully toss asparagus on opposite side with a drizzle of oil, salt, and pepper. Return to middle rack and roast until veggies are lightly browned and tender, 10-12 minutes more. (For 4 servings, leave potatoes roasting; add asparagus to a second baking sheet and roast on top rack.)

Heat a large drizzle of oil in pan used for onion over medium-high heat. Add steak and cook until browned and cooked to desired doneness, 3-6 minutes per side.

Turn off heat; transfer to a cutting board to rest for 5 minutes. 

If necessary, reheat saucy onion in the microwave, 15-20 seconds.

Toss asparagus with as much lemon zest as you like.

Slice steak against the grain.

Divide steak, asparagus, and potatoes between plates. Top potatoes with saucy onion and drizzle steak with as much horseradish cream as you like. Serve with remaining lemon wedges on the side.