Roasting butternut squash intensifies its flavor and reduces the prep work for this delicious, versatile lasagna. (use the time you save to wash and inspect the leeks, which may harbor bugs and tend to be quite dirty) the extra work spent cleaning the leeks is worth the effort--they impart a wonderful savory flavor to the bchamel sauce and make a great counterpoint to the sweetness of the squash. P. S. Don't be daunted by the lengthy leek-preparation instructions--the process is much simpler to do than it is to describe