Melt butter in large saucepan. Add onion and garlic; sauté until clear and soft. Add remaining ingredients using 1/4 tsp thyme. Bring to a boil; cover and simmer until vegetables are tender. Discard bay leaf. Add more thyme if desired. Purée hot soup on batches in a blender (careful of the splatter), or use immersion blender in the pot. Serves 6-8.