1. Cut asparagus tips and reserve, cut the rest of asparagus into 1/4-inch rounds: Cut tips from the asparagus 1 1/2 inches from top and reserve. Chop the rest of the asparagus stalks into 1/4-inch rounds.
2. Sauté onions, garlic: Melt the butter in a 4 to 5 quart pot on medium heat. Add the onions and cook until translucent, about 5 minutes.
Add the garlic (or green garlic) and cook a minute more.
3. Add asparagus: Add the chopped asparagus (not the spear tips) to the onions. Sprinkle with salt and pepper to taste. Cook another 5 minutes.
4.Add the broth, water, thyme sprigs and bay leaf to the pot. Increase the heat to a boil, then reduce to a simmer. Simmer, covered, until the asparagus are tender, about 10 minutes.
5. At the end of cooking, stir in the chopped parsley.
6. Blanch asparagus tips: While the soup is cooking, blanche the asparagus tips in a small pot of boiling, salted water, until the tips are just tender, about 2-4 minutes, depending on the size of the asparagus.
Drain. Rinse with cool water to stop the cooking. Set aside.
7. Purée the soup: Remove bay leaf and thyme sprigs. Use either an immersion blender or an upright blender (working in batches) to purée the soup.
8 Stir in cream, vermouth, lemon juice: Stir in the sour cream. Stir in the vermouth and lemon juice. Season with salt and pepper to taste.