Adjust racks to middle and top positions and preheat oven to 450 degrees. Wash and dry all produce. Halve and peel shallot. Finely chop one 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, 2 TBSP olive oil, garlic powder, and a couple large 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 10 minutes.

Meanwhile, toss green beans on a second baking sheet with a drizzle of olive oil, salt, and pepper. Once potatoes have roasted 10 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, 12-15 minutes.

While green beans 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, 4-6 minutes per side. Turn off heat; transfer to a cutting board to rest. Wipe out pan.

Heat a drizzle of oil in same pan over medium heat. Add shallot and cook, stirring, until softened, 1-2 minutes. Pour in 21/2 tsp vinegar (save the rest for another use). Simmer until reduced by half, 15-30 seconds. Stir in 1/4 cup water and stock concentrate. Simmer until thickened, 2-3 minutes. Turn off heat. Stir in sour cream and 1 TBSP butter. Season with salt and pepper.

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