Wash and dry all produce. Preheat oven to 425 degrees. Peel carrots, then cut on a diagonal into 1-inch-thick pieces. Trim, then thinly slice scallions, separating greens and whites. In a medium bowl, mix beef, scallion whites, meatloaf mix, 1/4 cup panko, and 1/4 tsp white pepper (we sent more panko and pepper). Season with salt (we used 1 tsp kosher salt) and a pinch of pepper.

Shape beef mixture into two 1-inch-tall loaves. Gently press down to flatten slightly. Toss carrots in another medium bowl with a large drizzle of oil, 1/2 tsp thyme (we sent more), salt, and pepper. Place carrots on one side of a baking sheet and meatloaves on other. Bake in oven on upper rack until meatloaves are cooked through, 20-25 minutes.

Meanwhile, cut potatoes into 1/2-inch cubes. Place in a medium pot with a big pinch of salt and water to cover by 1 inch. Bring to a boil and cook until tender, about 15 minutes, then drain and return to pot. Place over low heat, then add sour cream and 2 TBSP butter. Mash until smooth. Season with salt and pepper. Keep covered off heat.

While potatoes cook, halve, peel, and very thinly slice onion. Add slices to a large pan with a large drizzle of oil and place over medium-high heat. Cook, tossing often, until lightly browned and softened, about 5 minutes. Stir in a splash or two of water. Let water evaporate, 1-2 minutes. Repeat adding and evaporating water once or twice more until onion is deeply browned.

Once meatloaves and carrots are done, sprinkle meatloaves with mozzarella. Return to oven. Let cheese melt, 1-2 minutes; set aside. Add stock concentrate and 1/4 cup water to pan with onion. Bring to a boil over medium-high heat. Let reduce, 1-2 minutes. Remove from heat, then stir in 1 TBSP butter. Season with salt and pepper.

Give sauce a taste and stir in a pinch of sugar if you prefer a sweeter flavor. Divide potatoes, carrots, and meatloaves between plates. Spoon onion and its sauce over meatloaves. Garnish with scallion greens and serve.