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.

Lightly oil a baking sheet. In a large bowl, combine potatoes, 2 TBSP olive oil (4 TBSP for 4 servings), garlic powder, 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) and sprinkle with Gruyère. 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, place green beans on top rack. Roast until potatoes and green beans are tender and cheese is lightly browned, 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 until browned, 3-6 minutes per side. Turn off heat. Transfer steak to sheet with green beans; roast until cooked to desired doneness, 4-7 minutes. (TIP: If green beans are done before steak, remove from sheet and continue roasting steak.) Set aside to rest.

Wipe out pan used for steak; heat a drizzle of oil in same pan over medium heat. Add shallot; 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 1/4 cup water (1/3 cup for 4) and stock concentrate. 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 potato clusters, green beans, and sliced steak between plates. Top steak with sauce and serve.