This recipe is a great way to use up wilted lettuce or those outer leaves that have seen better days. don't use anything brown or slimy, though, as that will give the soup an off flavor.
3 tablespoons butter
3 cups chopped onion (about 3 medium)
2 tablespoons flour
3 cups diced potatoes
6 cups vegetable stock or 1 bouillon cube and 6 cups of water
1/2 teaspoon salt
6 cups chopped lettuce
2 egg yolks (save the whites to make meringues)
1/2 cup milk or cream
Melt the butter in a large soup pot over medium-high heat. Add the onion and cook until it has softened, 7 or 8 minutes. Add the flour and stir until it has been fully incorporated. Add the potatoes and stir to coat them with the butter. Add the salt, and vegetable stock or bouillon cube and water. Bring the soup to a boil, reduce the heat and simmer until the potatoes are soft, 15 to 20 minutes.
Add the lettuce. Cook until the lettuce is completely wilted but still green, about 5 minutes. Puree the soup with an immersion blender.
Just before you are ready to serve the soup, whisk together the egg yolks and milk or cream. While whisking, add a few ladlefuls of the soup and incorporate the egg mixture completely. Add the egg-soup mixture back into the soup pot and stir it in. If necessary, warm the soup over low heat, but do not allow it to simmer. Serve hot.