Chop leeks into thin rings and potatoes into cubes. Set aside.
Heat chicken broth in a large pot over medium heat. Add leeks and potatoes to pot and turn heat to low.
Place rosemary sprigs and bay leaf on top. Cover and let simmer for 30 minutes, or until potatoes are fork tender.
Remove rosemary sprigs and bay leaf. Pour broth, potatoes, and leeks into a large food processor or blender. Once smooth, add back to pot over low heat.
Add coconut milk and mix in slowly. Let simmer another 5 minutes.