Preheat oven to 425 degrees. Wash and dry all produce. Dice potatoes into ½-inch pieces. Place in a medium pot with enough salted water to cover by 2 inches. Boil until tender, 15-20 minutes. Reserve ½ cup potato cooking liquid, then drain and return potatoes to pot. Meanwhile, zest and halve lemon (halve both lemons for 4).

Pat chicken dry with paper towels; season all over with salt and pepper. Lay two slices of prosciutto beside each other on a flat surface. Tightly roll prosciutto around chicken. Repeat with remaining prosciutto and chicken.

Heat a drizzle of olive oil in a large pan over medium-high heat. Add chicken and sear until browned and crispy, 2-3 minutes per side. Transfer to one side of a baking sheet. Roast on top rack for 5 minutes (we’ll add the green beans then). (For 4 servings, spread chicken out across whole sheet and roast until cooked through, 15-17 minutes.)

Once chicken has roasted 5 minutes, remove baking sheet from oven. Toss green beans on empty side of same sheet with a large drizzle of olive oil, lemon zest, salt, and a pinch of chili flakes. (For 4 servings, toss green beans on a second baking sheet; roast on middle rack.) Roast until chicken is cooked through and green beans are tender, 10-12 minutes. (If chicken is done before green beans, remove from oven and continue roasting green beans.) Once cool enough to handle, slice chicken crosswise.

Meanwhile, finely chop chives. To pot with drained potatoes, add sour cream, half the chives, 2 TBSP butter, and as much truffle zest as you like. Mash until smooth, adding splashes of reserved potato cooking liquid as needed. Season with salt and pepper.

Heat pan used for chicken over medium-high heat. Add stock concentrate, ¼ cup water (⅓ cup for 4 servings), and lemon juice to taste. Cook until thickened, 1-2 minutes. Turn off heat; stir in 1 TBSP butter, salt, and pepper. Divide chicken, potatoes, and green beans between plates. Top chicken with sauce and remaining chives. Sprinkle green beans with more chili flakes if desired.