Heat butter in a large pot and sauté onions for 3-5 minutes. Add lettuce, pea shoots, peas, water and broth. Bring to a boil and simmer for 5 minutes on low heat.
Remove pan from heat and stir in chives. Puree soup with an immersion blender. Season to taste with salt and pepper.
Let cool 30 minutes and then chill, covered, for at least 3 hours before serving. Garnish with additional chives, if desired, and serve with a loaf of crusty bread. Enjoy!