Tarragon, garlic salt, and broth in 3½ to 4½ quart slow cooker. Cover and cook on low for 8 hours or on the high setting for 4 hours.
Puree in blender (1 cup at a time) until smooth. Add cream cheese to last batch of soup and continue to puree. Return pureed soup to crock pot , slow cooker. Stir half and half into soup and add pepper to taste.
Garnish soup with a swirl of half and half and a sprig of fresh tarragon.