Preheat the oven to 325 degrees . Season the beef with salt and black pepper. In a Dutch oven or other ovenproof pot, melt 2 tablespoons butter over medium-high heat. Add the beef and cook until browned, about 8 minutes. Using a slotted spoon, transfer to a bowl and set aside.
Add 2 tablespoons butter and the chopped onion to the pot and cook over medium-low heat, stirring occasionally, until the onion is golden-brown, 8 to 10 minutes. Whisk in the flour and cook for 1 minute. Slowly whisk in the wine, tomato paste and cayenne and bring to a boil, whisking occasionally. Return the meat and any juices to the pot and stir in the potatoes. Cover and transfer to the oven. Cook until the meat is fork-tender, 1 to 1-1/4 hours.
Meanwhile, in a medium skillet, melt the remaining 2 tablespoons butter over medium heat. Add the peas and pearl onions, sugar and a pinch of salt. Cook, stirring occasionally, until the liquid is almost cooked off. Stir the vegetables into the stew.
Scoop out the insides of each bread half, leaving a 3/4-inch border. Place each bread bowl on a dinner plate and fill with the stew.