Heat stock in a large saucepan, over medium heat. Add garlic and potato and cook over medium-high heat for 5 minutes.
Add Romaine, Iceberg and Boston lettuces to saucepan. Bring to a boil and reduce heat to medium-high. Cook until lettuce is wilted, about 5 minutes.
Remove garlic and add tomato sauce and cream.
In a blender, puree soup in batches. Return to saucepan and season with salt and pepper. Garnish each bowl with two bocconcini.