Adjust rack to top position (top and middle positions for 4 servings) and preheat oven to 425 degrees. Wash and dry produce.

Dice potatoes into ½-inch pieces. Trim and halve Brussels sprouts. Trim green beans if necessary. Halve, peel, and thinly slice shallot lengthwise. Trim and thinly slice scallions, separating whites from greens. Remove any pits from dates if necessary; halve lengthwise, then cut crosswise into ¼-inch-thick pieces.

Place potatoes in a medium pot with enough salted water to cover by 2 inches. Bring to a boil and cook until tender, 10-12 minutes.

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

Add half the sour cream and 1 TBSP butter (2 TBSP for 4 servings) to pot with potatoes. Mash until smooth and creamy, adding splashes of reserved potato cooking liquid as needed, until smooth and creamy. Taste and season with salt and pepper if desired.

Keep covered off heat until ready to serve.

While potatoes cook, toss Brussels sprouts on one side of a baking sheet with a drizzle of oil, salt, and pepper. (For 4 servings, spread Brussels sprouts out across entire sheet.) Roast on top rack for 5 minutes (you'll add more to the sheet then).

Once Brussels sprouts have roasted 5 minutes, carefully toss green beans on empty side of sheet with a drizzle of oil, salt, and pepper. Return to top rack and roast until browned and tender, 12-15 minutes. (For 4, leave Brussels sprouts roasting; toss green beans on a second baking sheet. Roast green beans on middle rack, swapping rack positions halfway through.)

Meanwhile, pat chicken* dry with paper towels; season all over with half the thyme (all for 4 servings), 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. Wipe out any burned bits from pan if necessary (leave the browned bits for flavor!).

Heat a drizzle of oil in pan used for chicken over medium heat. Add shallot and scallion whites; cook, stirring frequently, until shallot is browned and softened, 1-3 minutes.

Add vinegar and dates; cook, stirring and scraping up any browned bits, until vinegar has completely evaporated, 30-60 seconds.

Add ½ cup water (¾ cup for 4 servings), roasted onion and garlic spread, mustard, and stock concentrate. Cook, stirring frequently, until fully combined and sauce has thickened slightly, 1-2 minutes.

Turn off heat. Stir in scallion greens, remaining sour cream, and 1 TBSP butter (2 TBSP for 4) until fully combined.

Slice chicken crosswise.

Divide mashed potatoes, Brussels sprouts, green beans, and chicken between plates. Top chicken with shallot sauce and serve.