Adjust rack to top position and preheat oven to 425 degrees. Wash and dry produce.

Dice potatoes into ½-inch pieces. Trim green beans if necessary. Halve, peel, and finely dice half the onion (whole onion for 4 servings).

Place potatoes in a large pot with enough salted water to cover by 2 inches. Bring to a boil and cook until tender, 15-20 minutes. Reserve 1 cup potato cooking liquid, then drain.

Return potatoes to pot. Add sour cream and 2 TBSP butter (4 TBSP for 4 servings); mash until smooth and creamy, adding splashes of reserved potato cooking liquid as needed. Taste and season with salt and pepper if desired. Cover and set aside until ready to serve.

While potatoes cook, toss green beans on a baking sheet with a drizzle of oil, half the garlic powder, salt, and pepper. Roast on top rack until browned and tender, 12-15 minutes.

Cover with foil to keep warm until ready to serve.

Pat chicken* dry with paper towels; place between two large pieces of plastic wrap. Pound with a mallet or rolling pin until chicken is about ½ inch thick. Season all over with half the rosemary (all for 4 servings), remaining garlic powder, salt, and pepper.

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

Turn off heat; transfer to a plate and cover with foil to keep warm. Wipe out pan and let cool slightly.

Melt 1 TBSP butter (2 TBSP for 4 servings) in pan used for chicken over medium-low heat. Add diced onion; cook, stirring, until softened, 2-3 minutes.

Sprinkle onion with flour; stir until coated. Whisk in ½ cup water (1 cup for 4) and stock concentrate. Bring to a simmer and cook, stirring occasionally, until thickened, 2-3 minutes. TIP: If gravy seems too thick, stir in another splash of water.

Divide chicken, mashed potatoes, and green beans between plates. Spoon onion gravy over chicken and mashed potatoes. Serve.