Make the bisque:
Cover the bottom of a large cooking vessel with oil. When hot, add onion, carrots, and celery. Cook uncovered on medium high heat for 15 minutes or until vegetables are soft and volume is reduced by about one half. Add garlic and cook an additional 5 minutes.
Add remaining ingredients except half-and-half and lime zest. Cover and simmer 30 minutes or until sweet potatoes and apples are soft. Puree with an immersion blender. Stir in half-and-half and lime zest. Taste for seasoning and adjust. If a thinner bisque is desired, add water. Taste for seasoning and adjust. Add honey if needed.
Make the key lime cream:
Add cold whipping cream to a medium bowl. Whip with electric mixer until it begins to thicken. Add lime juice, powdered sugar, and 1 tablespoon lime zest. Whip until stiff peaks form. Add to hot bisque. Garnish with lime zest.