Heat 2 tablespoon oil in a large saucepan over medium heat. Add the carrots, onion and garlic and cook, stirring occasionally, until the vegetables are starting to brown at the edges 8 to 10 minutes. Add the spices and cook, stirring, for 1 minute.
Add the sweet potatoes, bouillon base, bay leaves and 6 cups water and bring to a boil. Reduce heat and simmer until the vegetables are very tender, 10 to 12 minutes.
Meanwhile, heat the remaining 2 tablespoon oil in a large skillet over medium heat. Add the bread and cook, tossing occasionally, until golden brown. Remove from heat, drizzle the maple syrup over the top and toss to coat.
Discard the bay leaves. Using an immersion blender (or standard blender in tow batches) puree the soup until smooth. Serve with the maple croutons.