Put the beef stock in a large saucepan over medium heat and bring to a boil. Cook until the liquid is reduced by half, leaving 4 cups.
Put the potatoes on a rimmed baking sheet and roast until just tender, about 45 minutes. When cool enough to handle, cut potatoes in half lengthwise and using a spoon, remove the potato flesh and reserve, leaving 1/2-inch thick rim around the edges. Drizzle 1 tablespoon of olive oil on the baking sheet and put potato shells on it, cut side down; bake until the cut side is golden brown and skin is crispy, about 20 minutes.
Pat the meat pieces dry with paper towels and season with salt and pepper. Heat 2 tablespoons of olive oil in a large Dutch oven and sear the beef on all sides to a deep golden brown, about 10 minutes. Remove the meat to a plate and carefully add a tablespoon of water to the hot pot, scraping up the brown bits from bottom of the pan. Add a tablespoon of olive oil and the pearl onions and season with salt and pepper, to taste. Cook about 7 minutes, stirring often, until the onions begin to caramelize, adding water, as needed, to deglaze the brown bits from the bottom of the pan. When the onions are a deep golden brown, add the reduced beef stock and the beef and their juices and bring to a boil. Reduce the heat to maintain a simmer and cook until the meat is tender, skimming fat off the top, if necessary, about 35 to 40 minutes.
Pass the reserved potato flesh through a ricer or mash with a masher until smooth, adding hot water to loosen them. Add 1 tablespoon olive oil, season with salt and pepper, to taste, and mix well.
Ladle the stew into the crisp potato bowls, top with a spoon of mashed potatoes and enjoy.