Adjust rack to middle position (middle and top positions for 4 servings) and preheat oven to 450 degrees. Wash and dry produce.

Dice potatoes into ½-inch pieces. Trim and halve Brussels sprouts lengthwise. Zest and quarter lemon. Peel and mince or grate ginger until you have 1 tsp (2 tsp for 4). Pick rosemary leaves from stems; mince leaves until you have 1 tsp. 

Place potatoes in a medium pot with enough salted water to cover by 2 inches. Bring to a boil and cook until tender, 15-20 minutes.

Reserve ½ cup potato cooking liquid, then drain and return potatoes to pot. Mash with sour cream and 1 TBSP butter (2 TBSP for 4 servings) until smooth and creamy, adding splashes of reserved potato cooking liquid as needed. Season with salt and pepper.

Keep covered off heat until ready to serve.

While potatoes cook, pat pork* 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 pork and sear, turning occasionally, until browned all over, 4-8 minutes (it’ll finish cooking in the next step).

Turn off heat; transfer pork to a plate. Wipe out pan.

Swap in chicken* for pork. Cook until browned and cooked through, 3-5 minutes per side. (No need to transfer to a baking sheet!)

Toss Brussels sprouts in a large bowl with a drizzle of oil, salt, and pepper. Spread out on one side of a baking sheet. Roast 5 minutes.  

Add pork to empty side of sheet. (For 4 servings, toss Brussels sprouts on a second sheet; roast pork on middle rack and Brussels sprouts on top rack.) Roast on middle rack until pork is cooked through and Brussels sprouts are tender, 10-12 minutes.

Transfer pork to a cutting board to rest. Carefully toss Brussels sprouts with lemon zest. 

Skip roasting chicken; spread Brussels sprouts across entire sheet.

Heat a drizzle of oil in pan used for pork over medium-high heat. Add minced ginger and minced rosemary; cook until fragrant, 30 seconds.

Stir in jam, stock concentrate, mustard, and ¼ cup water (⅓ cup for 4 servings). Simmer until slightly thickened, 2-3 minutes.

Remove from heat; stir in 1 TBSP butter (2 TBSP for 4) until melted.

Slice pork crosswise.

Divide pork, mashed potatoes, and Brussels sprouts between plates. Drizzle pork with sauce. Serve with lemon wedges on the side.

Slice chicken crosswise.