Melt butter in a large saucepan over medium heat. Add onions, ginger, and garlic. Season with kosher salt and freshly ground black pepper to taste. Stir frequently, don't brown the onions.
Add carrots, honey or sugar, baking soda, vegetable broth, and sprigs of thyme. Bring to a boil, reduce heat and simmer until carrots are fork tender, about 25 minutes.
Discard thyme sprigs. Process soup with an immersion blender until smooth. Stir in cider vinegar. Adjust seasonings as desired .