Preheat the oven to 375°F (190°C)
Boil lasagna noodles according to package instructions
Drain the noodles and set them aside
Cook ground beef or sausage in a skillet until browned
Add onion and garlic, then cook until softened
Stir in tomato sauce, tomato paste, salt, pepper, and Italian seasoning
Simmer the sauce for a few minutes
Mix ricotta cheese with egg, salt, and parsley
Grease a baking dish
Spread a thin layer of sauce on the bottom of the dish
Add a layer of noodles
Spread a layer of ricotta mixture over the noodles
Add a layer of meat sauce
Sprinkle mozzarella and Parmesan cheese over the sauce
Repeat the layers until ingredients are used up
Finish with sauce and a layer of mozzarella and Parmesan on top
Cover with foil and bake for 25 to 30 minutes
Remove foil and bake for 10 to 15 minutes more until bubbly and golden
Let the lasagna rest for 10 to 15 minutes before slicing
Serve warm