Coat a large saucepan with cooking spray, place over medium heat until hot. Add onion & garlic & saute 3 min. Or until tender. Add water, tomatoes, carrots, red potatoes & chicken bouillon granules. Bring to a boil. Cover, reduce heat & simmer 30 min. Or until carrots are tender; set aside. Position knife blade in processor. Add half of vegetables & cooking liquid. Process until smooth. Place in large bowl. Process remaining vegetables & cooking liquid. Add buttermilk, lemon juice, marjoram, thyme & white pepper to vegetable puree. Stir well. Cover. Chill 8 hours. Stir well before serving. Garnish with fresh thyme if desired. Serve chilled.