Adjust the rack to the middle position and preheat the oven to 400°F.

Wash and dry all produce.

Dice the potatoes into ½-inch pieces, thinly slice the chives, and trim and discard the woody ends from the asparagus.

Peel the garlic and place the whole clove in the center of a small piece of foil. Drizzle with olive oil and season with salt and pepper, then cinch into a packet.

Place the foil packet with garlic on a baking sheet and roast on the middle rack for 15 minutes.

Add the asparagus to the same sheet, toss with olive oil, salt, and pepper, and return to the oven until garlic is softened and asparagus is browned, about 10-12 minutes more.

Place the potatoes in a large pot with enough salted water to cover them by 2 inches. Bring to a boil and cook until tender, about 15-20 minutes.

Reserve ½ cup of potato cooking liquid, then drain and return the potatoes to the pot; mash until smooth.

Stir in sour cream, half the chives, salt, and pepper, adding reserved cooking liquid as needed until creamy.

Pat the steak dry with paper towels, season with salt and pepper, and heat oil in a large pan over medium-high heat.

Add the steak and cook to desired doneness, about 5-7 minutes per side. Transfer to a cutting board to rest.

Once the garlic is done, mash it with a fork until smooth.

Melt 1 tablespoon of butter in the pan used for steak, add garlic and cook for 1 minute.

Add demi-glace and ¼ cup water, simmer until slightly thickened, about 1-2 minutes. Stir in another tablespoon of butter and any resting juices from the steak, then season with salt and pepper.

Slice the steak against the grain. Divide the potatoes, asparagus, and steak between plates.

Top steak and potatoes with sauce, garnish with remaining chives, and serve.