Start by browning the sausage. You will do this in two batches. Divide the sausage meat. Pinch off pieces of sausage about ¼ to ½ inch in size and place them on the pan. I find this method easier than trying to chop the sausage with a knife or trying to break it up in the pan.
Heat the pan on medium heat. Allow the sausage to brown stirring from time to time. About 10 minutes. When done, remove to a plate lined with paper towels.
Repeat with the second batch of sausage.
In a large measuring bowl, beat the egg. Add all the ricotta cheese plus a quarter cup of parmesan cheese.
In a large saucepan on medium heat, heat the rest of the spaghetti sauce. Add the cooked sausage. Stir and keep warm.
Pour 1 cup of spaghetti sauce into a measuring cup. Add about ½ cup of hot water. Mix.
In a large 13x19 baking dish, pour the hot diluted sauce on to the bottom of the dish. Place noodles side-by-side on top to completely cover the sauce. You may need to break some of the noodles to achieve this.
Then put about ½ of the ricotta cheese mixture on top of the noodles. Put about ½ of the sauce making sure that the sausage is equally well arranged over the noodles. Top with half the mozzarella cheese. Then place the noodles and repeat with the ricotta, sauce and finish with a combination of mozzarella and parmesan. Make sure the top is completely covered. You should not see any of the sauce.
Cover and refrigerate overnight.
The next day, remove from the fridge.
Position a rack on the middle shelf of the oven. Preheat the oven to 350F. Once the oven is hot, place the lasagna in the middle and bake uncovered for 30 minutes until the edges start to turn a light brown.
Remove the lasagna from the oven and allow it to cool for at least 10 minutes.
Serve hot. Garnish with finely chopped fresh parsley if desired.
Note: Freezing lasagna leftover works very well. To do so, cut the lasagna into serving portion sizes and freeze. Make sure that the slices are separated so that they do not get stuck together. Use wax or parchment paper for this. To use, move slices from freezer to the fridge and thaw overnight. Then reheat in a toaster oven. You can use a microwave as well, but do so one slice at a time. Be sure to use a cover as the lasagna will splatter. Wipe the splatter off the plate before serving.