Melt the butter in a large heavy pot or Dutch oven over medium-high heat. Add the onions, celery, salt, and pepper. Cook, stirring often, until the onions are softened, 4† minutes. Add the garlic and bay leaves and stir until the garlic is fragrant, about 1 minute. Add the chicken stock and parsnips and bring to a boil. Reduce the heat to medium-low. Simmer, uncovered, stirring occasionally, for 1 hour.
Stir in the cream and vinegar. Remove and discard the bay leaves. PurČe the soup with an immersion blender or in batches in a food processor or blender.
Serve the soup hot in bowls, garnished with the bacon and chives.
Yield: 8 to 10 servings