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

Dice potatoes into ½-inch pieces. Halve and peel shallot; thinly slice one half and mince remaining. Trim and halve Brussels sprouts lengthwise.

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

While potatoes cook, in a large bowl, combine beef*, panko, minced shallot, half the garlic powder (you’ll use the rest later), and 1 TBSP water (2 TBSP for 4 servings); season generously with salt and pepper.

Form mixture into two 1-inch-tall loaves (four loaves for 4).

Place meatloaves on one side of a lightly oiled baking sheet. TIP: Line sheet with foil first for easier cleanup.

Toss Brussels sprouts on empty side with a drizzle of oil; season generously with salt and pepper.

Roast on top rack until meatloaves are cooked through and Brussels sprouts are browned and tender, 15-20 minutes. (For 4 servings, use 2 baking sheets; roast meatloaves on middle rack and Brussels sprouts on top rack.) TIP: If Brussels sprouts finish first, remove from sheet and continue roasting meatloaves.

While everything roasts, strip thyme leaves from stems; finely chop leaves until you have ½ tsp (1 tsp for 4 servings).

Heat a drizzle of oil in a medium pan over medium-high heat. Add chopped thyme and sliced shallot; season with salt and pepper. Cook, stirring, until softened, 2-4 minutes. 

Stir in demi-glace and ¼ cup water (⅓ cup for 4). Bring to a boil, then reduce to a low simmer. Cook until slightly thickened, 2-3 minutes.

Turn off heat. Stir in half the sour cream (you’ll use the rest in the next step) and 1 TBSP butter (2 TBSP for 4) until melted and combined. Season with salt and pepper.

Heat pot with drained potatoes over low heat; add remaining sour cream, remaining garlic powder, and 1 TBSP butter (2 TBSP for 4 servings).

Mash until smooth and creamy, adding splashes of reserved potato cooking liquid as needed. Season with salt and pepper.

If necessary, reheat pan with sauce over low heat; stir until warmed through.

Divide meatloaves, mashed potatoes, and Brussels sprouts between plates. Spoon sauce over meatloaves and serve.