Note 1: If you are making this dish ahead you can refrigerate the mash mixture at this point up to 2 days ahead. Keep the reserved cooking liquid and frizzled leeks well sealed too. Reheat potatoes slowly on top of stove or in the oven. When the potatoes are warm, if they are too dry - add more warm reserved liquid and stir vigorously to incorporate smoothly before serving. Gently warm frizzled leeks in microwave, top the potato mash and serve.