Melt the butter in a large pan overmedium low heat. Add the onion, leeks, and rice. Cover and cook stirring accasionally for about 10 minutes until the vegetables are softened.
Add he peas, water, bouillin cube, and arragon and bring just to a boil. Season a little pepper. Cover an simmer gently occasionally stirring for about 35 minutes until the vegetables are very tender.
Let the soup cool slihtly, then transfer to a blender or food processor and process to a smooth puree in batches if necessary. (If using a food processor strain of the coooking liquid and preserve. Puree the soup solids with enough cooking liquid to moisture them, then combine with the remining liquid.)
Return the soup to the pan. Taste and adjust the seasoning. Gently reheat the soup over low heat for about 10 minutes until hot.
Ladle into warm bowls and garnish with hard cooked egg or crootons.