Leek and Potato Soup

Aren't these leeks adorable?  So pretty and make such a nice soup.  I found this recipe in a Mexican Cookbook and just use regular chicken broth instead of the suggested Mexican chicken broth.  I have had it both ways, equally tasty.  Heat 3 T.butter and 2 T. veggie oil over medium-low heat until butter melts and begins to foam.  Add leeks and cook leisurely for 15-20 minutes, stirring occasionally, until completely soft and beginning to brown.   Stir in broth, potatoes, salt and pepper to taste.  Bring heat to high then simmer and cook until potatoes are tender.  You can thicken the soup by scooping out 1 cup with at least 1/2 cup of potatoes in it and puree in a blender then return it to the pot, or you can puree the whole batch and have a cream of leek and potato soup.  It's good.  Here are the requirements. 3 T. butter, 2 T. vegetable oil, 4 C. thinly sliced leeks (white and light green parts only) 8 C. chicken or vegetable broth, 4 C. peeled-cubed (1/2 inch) potatoes.  Salt and pepper to taste.  From the book, "Pati's Mexican Table" Pati Jinich