In a large pot of boiling salted water, cook lasagna noodles according to package instructions.
Heat olive oil in a large cast iron skillet over medium high heat. Add ground beef and onion and cook until beef has browned, about 3-5 minutes, making sure to crumble the beef as it cooks; season with salt and pepper, to taste. Drain excess fat.
Stir in tomatoes and Italian seasoning. Bring to a boil; reduce heat and simmer until thickened, about 10-15 minutes.
In a medium bowl, combine ricotta, 1/2 cup mozzarella and egg; set aside.
Preheat oven to 350 degrees F. Lightly oil a 9 x 13 baking dish or coat with nonstick spray.
Spread 1 cup tomato mixture onto the bottom of a 9×13 baking dish; top with 3 lasagna noodles, 1/2 of the ricotta cheese mixture and 1 cup mozzarella cheese. Repeat with a second layer. Top with remaining noodles, tomato mixture, 1 cup mozzarella cheese and Parmesan.*
Place into oven and bake for 35-45 minutes, or until bubbling. Then broil for 2-3 minutes, or until top is browned in spots. Let cool 15 minutes.
Serve, garnished with parsley, if desired.
Notes
Reduce the sauce. Gently simmer the meat sauce for 10-15 minutes (for a quick weekday version), stirring the pot occasionally to prevent sticking. The sauce should be thick, not watery. If it is too wet, the lasagna will be soggy. When time permits, simmer for 1-2 hrs, allowing the flavors to really meld and marry.
Use no-boil lasagna noodles. To cut down on prep time even more, use no-boil lasagna noodles, making sure the noodles are completely covered in sauce prior to baking.
Mix it up. This recipe uses ground beef for budget-friendly convenience but a mixture of lean ground beef and sweet Italian sausage should work very well here.
Avoid fresh mozzarella. Use low-moisture, whole milk mozzarella cheese. Fresh mozzarella will have too much liquid, resulting in a watery lasagna.
Cover with foil. If the lasagna is browning too quickly, cover with foil, spraying the foil with nonstick spray first so the cheese does not stick.
Let it rest. Let the lasagna sit for 10-15 minutes. This will prevent the layers from sliding off, and will also make it easier to serve with less mess.
Make ahead of time. Lasagna is a great dish to make ahead of time. Prep and assemble 1-2 days before, covered with aluminum foil and stored in the fridge.
Freeze before baking. This will preserve the texture and prevent sogginess. Always use a freezer-safe baking dish, label, date and freeze up to 3 months.