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

Dice potatoes into ½-inch pieces. Cut broccoli into bite-size pieces if necessary. 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 until lightly browned and tender, 20-25 minutes.

Meanwhile, pat chicken* dry with paper towels and 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, 3-5 minutes per side.

Turn off heat; transfer chicken to a cutting board to rest.

While chicken cooks, toss broccoli on a second baking sheet with a drizzle of oil and a pinch of salt and pepper.

Roast on middle rack until tender, 12-15 minutes.

Heat pan used for chicken over medium heat. Stir in stock concentrate, 2 TBSP water (4 TBSP for 4 servings), and as much chopped dill and mustard as you like.

Remove pan from heat; stir in sour cream and 1 TBSP butter (2 TBSP for 4), scraping up any browned bits from bottom of pan. Season with salt and pepper. TIP: If sauce seems too thick, add more water 1 tsp at a time until it reaches a drizzling consistency.

Slice chicken crosswise.

Divide chicken, potatoes, and broccoli between plates and drizzle with sauce. Garnish with any remaining chopped dill if desired and serve.