Remove root and green tops from leeks. Slice in half lengthwise and rinse well under running water. Slice crosswise into ¼ inch slices.
Scrub potatoes under running water with a clean vegetable brush; cut into small cubes.
Melt margarine or butter in a 2-quart saucepan over medium heat.
Add garlic and chopped leeks. Cook until softened.
Add potatoes and enough broth to cover. Cover pan and simmer until potatoes are soft. Mash with a potato masher or fork until potatoes are fairly smooth.
Add remaining broth, milk and pepper. Simmer for about 5 minutes.
Refrigerate leftovers within 2 hours.
Source: FoodHero.org, recipe/ Creamy Potato and Leek Soup