Heat the oil in a large saucepan over medium-high heat. Add the onion and cook, stirring occasionally, until softened but not browned, 5 to 6 minutes. Stir in the carrots, broth, ginger, 1 1/4 teaspoons of the salt, and the pepper. Bring to a boil. Reduce heat and simmer until the carrots are soft, about 20 minutes. Let cool at least 10 minutes.
Using a blender, puree the soup in batches until smooth. Return to pot and rewarm over medium heat.
Meanwhile, whisk the cream in a small bowl until soft peaks form. Fold in the remaining salt and the dill. Divide the soup among individual bowls and top with the dill cream.
Tip: Tightly wrap any leftover ginger in plastic and store it in the freezer, where it can last up to a month. No need to thaw; you can slice or grate frozen ginger.