To make the soup, chop the onions and leeks, and cut the potatoes into cubes. Melt the butter in a medium saucepan, then add the vegetables and leave to soften for 4–5 minutes, stirring occasionally. Add the vegetable stock to the pan and leave to simmer for 15–20 minutes with the lid on.
Blend or mash the soup until smooth, season to taste and pour into bowls. Serve with breadcrumbs, fresh bread and pieces of cheese.
