How to Make It
Preheat the oven to 400 degrees. In a roasting pan, add the brussels sprouts and carrots, then drizzle with 1 tablespoon of the olive oil. Roast until dark and caramelized, about 50 minutes, then set aside.
As the vegetables roast, boil the potatoes. Add them to a pot and fill with enough water to cover by 1 inch; boil until tender, about 15 minutes. Strain and mash with 4 tablespoons of butter, white pepper and salt; set aside.
Warm a skillet or pan over medium heat, then add the remaining olive oil and butter and warm for 1 minute. Add the onion and sauté until softened, about 4 minutes, then add the potatoes and winter vegetables. Mash the vegetables together, then gently pat into a thick pancake. Pan-fry until browned on the bottom, about 25 minutes, then flip and mash together. Pat flat and pan-fry again until brown and crispy, another 25 minutes, then mash once more. Season with salt and pepper to taste and serve.