melt butter in large saucepan over low heat

stir in onion and leeks

cover and cook 20 minutes

stir in potato, cover and cook 15 minutes

stir in broth, salt, and pepper, bring to boil

reduce heat, and simmer 30 minutes or until potato is tender

remove from heat and cool slightly

process soup in batches in blender until smooth....stopping to scrape down sides

return to saucepan and cook over medium heat until thoroughly heated

serve with toppings