Soak the barley for several hours or overnight, then drain and simmer in plenty of salted water until soft. Drain the barley, but keep the cooking water. Rinse and drain the beans, then puree them in a blender with a cup of barley cooking water.
Finely slice the onion and leek. Coarsely grate the carrots and finely grate the garlic. Heat the oil over medium heat in a large, heavy-based pan. Add the vegetables and let them sweat until soft. Add the pasta sauce, followed by the bean puree and up to three cups of barley cooking water (depending on how thick you want the soup).
Bring soup to a boil, then reduce heat and simmer gently, stirring occasionally. After 15 minutes add the cooked barley, and keep simmering for another 15 minutes. Season to taste, and serve with crusty bread.
Source of recipe: Based on Giorgio Locatelli's Mixed Bean & Farro Soup: http://uktv.co.uk/food/recipe/aid/511723 [1]