- In a large soup pot over high heat, combine the potatoes, asparagus, onions, celery and water.
- Bring to a boil. Reduce heat, cover and simmer until the vegetables are tender, about 15 minutes. Stir in the butter.
- In a small bowl, whisk together the flour and milk.
- Pour the mixture slowly into the soup pot, stirring constantly. Increase the heat to medium high and continue to stir until the soup thickens, about 5 minutes.
- Remove from heat. Season with lemon peel and cracked black pepper to taste.
- Serve in warmed bowls