Adjust racks to top and middle positions and preheat oven to 450 degrees. Wash and dry produce.

Dice potatoes into ½-inch pieces. Pick and finely chop fronds from dill.

Toss potatoes on a baking sheet with a drizzle of oil and a pinch of salt and pepper.

Roast on top rack, tossing halfway through, until lightly browned and tender, 20-25 minutes.

While potatoes roast, pat chicken* dry with paper towels; season all over with salt and pepper.

Heat a drizzle of oil in a large pan over medium-high heat. Add chicken and cook until browned and cooked through, 5-7 minutes per side.

Turn off heat; transfer to a cutting board and set aside to rest.

While chicken cooks, trim green beans if necessary; toss on a second baking sheet with a drizzle of oil and a pinch of salt and pepper.

Roast on middle rack until tender, 10-12 minutes.

Meanwhile, in pan used for chicken, combine stock concentrate and ¼ cup water (⅓ cup for 4 servings); bring to a simmer over medium-high heat, 1-2 minutes.

Reduce heat to low and whisk in sour cream, half the chopped dill, and mustard to taste. Turn off heat.

Stir in 1 TBSP butter (2 TBSP for 4) and any resting juices from chicken. Season with salt and pepper.

Slice chicken crosswise.

Divide chicken, potatoes, and green beans between plates. Drizzle sauce over chicken. Garnish with as much remaining chopped dill as you like and serve.