Many lettuces are grown in sandy soil, so thoroughly wash and dry your greens to remove any grit. If you don't have an immersion blender, process the soup in batches in a blender until smooth.
How to Make It
Rinse romaine, escarole, and butter lettuce well; shake and pat dry. Roughly chop leaves and stems; discard cores.
Melt butter in a large Dutch oven over medium. Add leeks and garlic; cook, stirring occasionally, until softened, 4 to 5 minutes. Add wine, and cook 1 minute. Stir in lettuces, stock, and beans. Cover and increase heat to medium-high; bring to a boil, stirring occasionally. Reduce heat to low, and simmer, covered, until lettuce leaves are wilted and stems are softened, 8 to 10 minutes. Remove from heat; stir in sour cream, parsley, and dill.
Using an immersion blender, process hot soup until smooth. Stir in salt and pepper. Garnish servings with sour cream and dill sprigs, if desired.