Makes 8 cups. Freezes well.
Cut bacon into 1/4-inch slices (scissors are easiest for this) and place in a cold soup pot. Heat the pot over medium-high heat and cook the bacon until it's crisp. Remove with a slotted spoon to a plate covered with paper towels and set aside to drain and crisp.
Keep 1 tablespoon of the fat in the pan and discard the rest. Re-heat the fat over medium-high heat, then add the onions, Ras el Hanout, salt, pepper, and cayenne. Cook, stirring occasionally, until the onions are soft, about 5-7 minutes. Toss in the garlic and stir, cooking until fragrant, about 30 seconds.
Add the sweet potatoes, broth, and water to the pot. Bring to a boil, reduce heat to simmer, cover, and cook until the potatoes are tender, about 10-15 minutes.
Purée the soup with an immersion blender until smooth. Ladle into bowls and sprinkle with bacon bits and chives.