Soak the prunes in warm water for at least 30 minutes, or the entire time the tagine cooks.
Season the beef with salt and pepper. Heat the oil in a large Dutch oven over medium-high heat. Sauté half the meat, uncovered, stirring only occasionally, until well browned, about 8 minutes. Using a slotted spoon, transfer the beef to a plate. Repeat with the remaining beef.
Lower the heat to medium and add onions to the Dutch oven. Sauté until softened, about 4 minutes. Add the garlic, ginger, cinnamon, cumin, coriander, turmeric and saffron, and sauté for another minute or until fragrant.
Add the reserved beef to the pan, along with 2 cups water, butternut squash and cilantro. Cook, partially covered, stirring occasionally, until the liquid thickens and the meat and vegetables are tender, about 2 to 2 1/2 hours, adding a little more water if the stew appears too dry. Season with more salt and pepper to taste, if necessary.
Transfer stew to a serving bowl or platter and garnish with the prunes and the almonds.