Cream of Potato Soup

It might not be very exciting, but I find that when fall starts appearing I always want potato soup.  I have a lot of variations that I make, but this is the most basic.  It is just simply good.

Serves 3-4

1 tablespoon butter
1 large or 2 medium leeks, chopped small
5 potatoes, cubed
2 cups water
3 tablespoons flour
1 cup milk
Dash ground mustard
Salt and ground black pepper to taste

1. In medium saucepan, melt butter over medium heat.  Add leeks and saute until tender.  Add potatoes and stir until leeks coat potato cubes.  Pour water over potatoes and bring to a simmer.  Simmer potatoes and leeks until potatoes are tender.
2. Meanwhile, mix flour and milk together in a measuring cup.  When potatoes are tender, add milk mixture to potato mixture in saucepan and stir well.  Return soup to just a simmer until soup thickens.  Add ground mustard, salt, and pepper.  Serve immediately.