Wash your leeks thoroughly. The easiest way to do this is to slice them lengthwise, and then into half-moons. Then, put them in a bowl of water and agitate them with your hands. Rinse them in a colander. I repeat this process until there is no silt on the bottom of the bowl.
Melt butter in a medium skillet over low heat and add leeks. Cover and let them cook for 7-10 minutes until soft, but not browned.
Add garlic and let cook for 1 minute.
While leeks and garlic are cooking, add potatoes, broth, salt and pepper to your slow cooker and stir to combine. For added protein, you can add a can of drained white beans and an additional cup of water or broth.
Add sauteed leek and garlic mixture.
Cover and cook on low for 8-9 hours or high for 4-5 hours.
Use a hand held blender or immersion blender to blend the soup while still in the slow cooker. You can either puree it all or just part of the soup so that some chunks still remain.
Serve as is, with a dollop of sour cream, a swirl of Leek Oil, or a sprinkling of chives.