Adjust rack to upper position and preheat oven to 425 degrees. Wash and dry all produce. Halve potatoes, then cut into 1/2-inch-thick wedges. Trim and peel carrots, then cut into 1-inch pieces on a diagonal. Pat steak dry with paper towels; season all over with salt and pepper. Let sit at room temperature until ready to cook.

Place potatoes and carrots on opposite sides of a baking sheet. (For 4 servings, use two baking sheets; roast potatoes on top rack and carrots on middle rack.) Toss each with a drizzle of olive oil and a pinch of salt and pepper. Roast until browned and tender, about 30 minutes.

Meanwhile, trim and thinly slice scallions, separating whites from greens. Halve, peel, and finely chop shallot. In a small bowl, combine sour cream, a drizzle of olive oil, and truffle zest (start with a pinch, taste, and add more from there). Add water, 1 tsp at a time, until mixture reaches a drizzling consistency.

Pat steak dry with paper towels again. Heat a drizzle of olive oil in a large pan over medium-high heat. Add steak and cook until nicely browned on first side, 3-6 minutes. Flip and lower heat to medium. Add 1 tsp Herbes de Provence (2 tsp for 4 servings; we sent more) and 2 TBSP butter (4 TBSP for 4) to pan. Carefully tilt pan toward you. Using a spoon, continually baste steak with butter until it reaches desired doneness, 6-9 minutes more.

Transfer steak to a cutting board and let rest, keeping any remaining butter in pan. Place same pan over medium-high heat and add scallion whites and shallot. Cook, stirring, until softened, 3-4 minutes. Meanwhile, combine stock concentrate and 2 TBSP water (1/4 cup for 4 servings) in a separate small bowl. Pour into pan and let simmer until slightly thickened, about 1 minute.

Thinly slice steak against the grain. Divide sliced steak, potatoes, and carrots between plates. Stir any resting juices from steak into pan sauce. Drizzle sauce over steak and garnish with scallion greens. Serve with truffle cream on the side for dipping.