Adjust racks to middle and top positions and preheat oven to 450 degrees. Wash and dry all produce. Halve and peel shallot; finely chop half (save other half for another use). Slice potatoes into 1/4-inch-thick rounds (no need to peel).

Lightly oil a baking sheet. In a large bowl, combine potatoes, garlic powder, 2 TBSP olive oil (4 TBSP for 4 servings), and a couple big pinches of salt and pepper; toss until potatoes are completely coated. Arrange potatoes on prepared sheet into clusters (about 6 slightly overlapping slices each). Roast on middle rack for 12 minutes.

Meanwhile, toss green beans on a second baking sheet with a drizzle of olive oil, salt, and pepper. Once potatoes have roasted 12 minutes, remove from oven and sprinkle with Parmesan. Return to middle rack and place green beans on top rack. Roast until potatoes are tender, cheese is lightly browned, and green beans are tender, 10-12 minutes more.

While veggies roast, pat steak dry with paper towels; season all over with salt and pepper. Heat a large drizzle of oil in a large pan over medium-high heat. Add steak and cook to desired doneness, 5-7 minutes per side. Turn off heat; wipe out pan. Transfer to a cutting board to rest.

Heat a drizzle of oil in pan used for steak over medium heat. Add shallot and cook, stirring, until softened, 1-2 minutes. Pour in half the vinegar (use all for 4 servings). Simmer until reduced by half, 15-30 seconds. Stir in stock concentrate and 1/4 cup water (1/3 cup for 4). Simmer until thickened, 2-3 minutes. Turn off heat. Stir in sour cream and 1 TBSP butter (2 TBSP for 4). Season with salt and pepper.

Slice steak against the grain. Divide steak, potato clusters, and green beans between plates. Top steak with sauce and serve.