3 tbs butter
3 leeks, thinly sliced
1 onion, chopped
6 - 8 russet potatoes, thinly sliced
4 cups chicken broth
1 cup heavy cream
salt and pepper to taste
Melt butter in a large saucepan over medium heat then add onions and leeks. Cook, stirring, until onions are limp and are starting to brown.
Add sliced potatoes to saucepan then pour in enough chicken broth to just barely cover the potatoes. Continue cooking over medium heat until potatoes are tender. Mash and stir potatoes until desired consistency is reached. As you mash the potatoes and the soup thickens, turn down heat and stir often.
Add one cup of heavy cream and salt and black pepper to taste. Cook 15 minutes more over low heat, stirring frequently, then remove from heat and serve.