Heat oil in a large pot over medium-low heat and cook onions until soft and translucent, about 5 minutes. Add garlic and cook until fragrant, about 1 minute. Stir in carrots and cook until softened, 3 minutes more. Pour in vegetable broth and bring to a boil. Season with ginger, salt, pepper, and sugar. Cover, reduce heat, and simmer until vegetables are soft and cooked through, about 15 minutes.
Puree carrot soup with an immersion blender until smooth. Add heavy cream and heat through. Puree once more quickly with immersion blender, and season with salt and pepper.