Recipe courtesy Gabriele Corcos and Debi Mazar. Notes: Because you are working with pasta that does not require boiling, you have to make sure that there are no pieces of lasagne sticking out of the sauce because they won't cook. When you decide to tap into your reserve of frozen lasagne, keep in mind you need to thaw the frozen lasagne overnight before reheating. If the sauce is too thick, add a little more milk, if too runny, return to the heat and add a pat of butter mixed with an equal amount of all-purpose flour. The most important thing though is: besciamella should not taste floury. If you think your sauce is ready, but you can spot a hint of "flouriness" when you taste it, think again, and keep on cooking it for a few minutes more.