Stir in ground cumin, coriander, and cayenne pepper, followed by vegetable broth and chopped sweet potatoes and apple. Season with salt and black pepper.
Bring to a boil, reduce heat to low, cover, and simmer for 20-25 minutes until sweet potatoes are tender.
Blend the soup until smooth using an immersion blender or regular blender; return to pot if needed.
Stir in heavy cream or coconut milk for creaminess, adjust seasoning if necessary, and gently heat through before serving.