Melt butter in large saucepan over medium heat. Add onions, ginger, and garlic. Season with kosher salt to taste; cook, stirring frequently, until onions are softened but not browned.
Increase heat to high; add carrots, sugar, broth, thyme sprigs, and baking soda. Bring to a boil, reduce heat to medium-low and simmer, until carrots are very tender, 20 to 25 minutes.
Discard thyme sprigs. Working in batches, process soup in blender until smooth. Return soup to pot and stir in vinegar. Return to simmer over medium heat and season with salt and pepper to taste.
Recipe by the minimalist table at https://www.daraboxer.com/theminimalisttable/carrot-ginger-soup/