Step 1In a heavy stockpot, heat the oil over medium heat. Add the onion and cook until translucent, about 5 minutes, stirring occasionally.
Step 2Stir in the garlic, cumin, coriander, ginger and cayenne. Continue cooking until the onion is soft.
Step 3Stir in the carrots, sweet potato and broth. Cover and simmer until carrots are very tender, about 20 minutes. Using an immersion blender, or in batches using a stand blender, purée the soup until smooth.
Step 4Stir in the orange juice, and thin to desired consistency with additional orange juice, vegetable broth or water. Adjust the spices if desired, and season to taste with salt and pepper. This makes about 3 quarts soup. Garnish each serving with chopped cilantro.