Potato Leek Soup

This is a great soup to make a ton of and have on hand all week. It requires only three ingredients (one of which is butter) so it's a good one to try if you're at the store and don't want to run all over getting ingredients. I like to make as much as I can, using roughly equal parts leeks and potatoes.

Russet Potatoes, peeled and chopped
Leeks, trimmed, washed well, and sliced

Put chopped leeks and potatoes into large pot and cover with water. Bring to boil and simmer till potatoes are done (about 45 minutes). Mash with a fork until smooth. Add some big hunks of butter and salt to taste.