This luxurious, silky smooth potato soup showcases a brilliant emerald mound of pesto floating on the surface -- perfect for St. Patrick's Day dinners. Make the pesto ahead of time. If you can't obtain enough fresh basil, look for a good quality jarred pesto for this recipe. Crème fraiche is often available at a good cheesemonger or in some specialty food shops. You can easily make your own, though. Serve this soup with thin slices of toasted baguettes.