Bring a saucepot of water to a boil, then boil the onions for 3 to 4 minutes, drain and cool. Squeeze pearl the onions from the skins, pushing with root end facing away from you.
Pat the meat dry and sprinkle liberally with salt and pepper. Heat the oil, 2 turns of the pan, in a large Dutch oven over medium-high heat. Add the meat and brown evenly all over, then remove to a plate and lower the heat to medium. Add the butter and melt, then add the garlic and onions. Season with salt and pepper. Cook, stirring, until lightly brown, a few minutes. Stir in the tomato paste and cook for 1 minute, then add the wine to deglaze. Add the beef, stock and tomatoes. Combine and roast, covered, until tender, 2 to 2 1/2 hours. Cool and store for a make-ahead meal. Reheat on the stovetop over medium heat, stirring frequently.
Serve with the bread for mopping, and garnish with the parsley.