I found this recipe on allrecipes.com
Slicing into lasagna immediately after it leaves the oven guarantees a collapsed, watery mess on the plate. Water accumulates inside baked layers when hot cheeses and simmering tomato sauces release internal moisture without adequate resting time. Letting the casserole sit for fifteen minutes allows dairy fats and starches to firm up, yielding clean, distinct portions. Sweet Italian sausage and lean ground beef render considerable fat during the initial ninety-minute Dutch oven simmer, so skimming excess grease from the meat sauce prevents a greasy surface pool. Fennel seeds and dried basil require that extended simmer to hydrate fully and soften their cell walls, releasing aromatic compounds into the tomato paste and crushed tomatoes without leaving hard fragments in the finished dish. Rinsing boiled noodles in cold water halts starch gelatinization immediately, stopping the pasta from turning mushy before assembly. Spraying the underside of the aluminum foil with cooking spray stops melted mozzarella from welding itself to the metal during the initial covered bake at 375 degrees Fahrenheit. Removing that foil for the final twenty-five minutes of baking encourages surface evaporation, browning the grated Parmesan cheese and rendering the top mozzarella layer chewy rather than rubbery.
Pasta sheets absorb liquid continuously while baking. Undercooking the noodles slightly during the initial eight to ten minute boil gives them structural integrity against the heavy meat sauce and ricotta mixture. Ricotta cheese contains high water content; binding it with a raw egg provides the necessary protein matrix to set the cheese layer into a firm curd during thermal exposure. Slicing mozzarella cheese manually instead of using pre-shredded varieties avoids anti-caking cellulose powders that interfere with smooth melting.