1. Warm oil in a large saucepan over medium-high heat. Add onion and cook, stirring often, until softened but not browned, 3 to 5 minutes. Add garlic and ginger and sauté 1 minute longer. Add carrots, pour in broth and season with a pinch of salt. Increase heat to high and bring to a boil. Reduce heat to medium and cook, partially covered, stirring occasionally, until carrots are very tender, 25 to 30 minutes. Remove from heat and let cool slightly.
2. Working in batches, puree soup in a blender. Return soup to pot and bring to a simmer. Stir in lime juice and cream and season with salt and pepper. Do not boil. Thin with additional broth or water if soup is too thick.
3. Let cool, cover and refrigerate until ready to use. Ladle into a thermos cold, or, to serve warm, rewarm over medium-low heat, stirring often, before ladling into thermos.