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

Halve and core apple; dice one half into ¼-inch pieces (dice whole apple for 4 servings). Strip rosemary leaves from stems; roughly chop leaves until you have 1 tsp (2 tsp for 4).

Heat a drizzle of olive oil in a large pan over medium-high heat. Add diced apple and chopped rosemary. Cook, stirring occasionally, until apple is slightly softened, 4-6 minutes.

Stir stock concentrate, ½ cup water (¾ cup for 4 servings), and 1 tsp sugar (2 tsp for 4) into pan with apple mixture. Bring to a simmer, then reduce heat to medium. Cook until apple is tender and liquid has reduced, 8-10 minutes.

Turn off heat; stir in half the mustard (all for 4) and 1 TBSP butter (2 TBSP for 4) until melted and combined. Season with salt and pepper.

Transfer to a medium microwave-safe bowl and cover to keep warm. Wash out pan.

Meanwhile, trim and halve Brussels sprouts lengthwise. Toss on a baking sheet with a drizzle of olive oil, salt, and pepper.

Roast on top rack until browned and tender, 15-20 minutes.

While Brussels sprouts roast, dice potatoes into ½-inch pieces. Place in a medium pot with enough salted water to cover by 2 inches. Bring to a boil and cook until potatoes are tender, 15-20 minutes.

Reserve ½ cup potato cooking liquid, then drain and return potatoes to pot.

Mash with sour cream, 1 TBSP butter (2 TBSP for 4 servings), salt, and pepper until smooth, adding splashes of reserved potato cooking liquid as needed.

Keep covered off heat until ready to serve.

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

Heat a drizzle of olive oil in pan used for sauce over medium-high heat. Add pork and cook until browned and cooked through, 4-6 minutes per side.

Swap in chicken* for pork; cook until cooked through, 3-5 minutes per side.

Divide Brussels sprouts, mashed potatoes, and pork between plates. Top pork with apple pan sauce and serve. TIP: If sauce has cooled, reheat in microwave for 30 seconds or return to pan with a splash of water; cook over medium heat, stirring, until warm.