This is a crowd pleaser that will have your family (or guests) heading back for seconds. When in doubt, err on the side of excess; you can always freeze the sauce or an entire additional lasagna for an easy freezer meal down the road.
Prepare sauce first at least an hour ahead of time. Dice onions and add to a large pot, along with ground beef and a dash of garlic salt. Cook over medium heat until beef is browned all the way through. Stir occasionally, breaking up larger clumps of beef. Try to make the meat as "fine" as possible as it is cooking.
Once the meat is browned, drain and discard the grease. Add tomatoes, tomato sauce **(LEAVE approx. 1/5-2 cups of the spaghetti sauce in the jar for a future step!)**, 1 Tbsp. garlic salt, 2 tsp. oregano, and 2 tsp. italian seasoning to pot. Stir together, cover, and simmer for at least one hour. Stir occasionally.
When the sauce is finished, boil 10 lasagna noodles (in salted water) for 10 minutes, drain and set aside.
While the noodles are boiling, start preparing the cheese mixture. In a large mixing bowl, combine the 16 oz. ricotta cheese, 3 cups of the mozzarella cheese, 1 cup of the parmesan cheese, 1/2 cup of milk, 1/2 cup of remaining jar spaghetti sauce, and garlic salt and parsley flakes (to taste) - the consistency should be more like "dough" and less like "batter" (wet but not runny)
Now that your sauce is prepared and your cheese mixture is ready, preheat oven to 375° Spread a VERY thin layer of jar spaghetti sauce on the bottom of a 9x13 baking dish, just enough so the noodles won't stick.
Arrange noodles vertically in the dish, starting at the side. As you add noodles, slightly overlap; there should be 4 across when finished. Break off 3/4 of a noodle and add it to the short end where the gap is.
Spoon 1/2 of cheese mixture onto noodles and press as you spread and distribute. The layer will be 1/4-1/2" thick. Again, the consistency should not be runny.
Once the cheese mixture is covering the noodle layer, spoon meat sauce layer onto the cheese layer. SPOON instead of POURING.
Add second (and final) layer of noodles in the same manner as the first layer.
Spoon second half of cheese mixture on top of the lasagna noodle layer. Press and spread as before.
Spoon meat sauce on the cheese layer as before. (The remaining meat sauce mixture can be placed divided (or stored together) into food storage containers and frozen for future, easy spaghetti dinners.
For the top layer, sprinkle 1 cup remaining mozzarella and 1/2 cup remaining parmesan evenly. Add a few dashes of parsley flakes on top.
Bake lasagna for 25 minutes (until bubbling and top begins to brown)
After lasagna is finished, slightly brown the top by setting the oven to "broil" for a couple of minutes. DO NOT WALK AWAY as it is very easy to burn during this step. Remove from over after 2 to 3 minutes.
Allow to set for a few minutes before serving.
The meat sauce quantity in this recipe is intended for spaghetti sauce leftovers which can be frozen.