Boil water in a large pot.
Add salt to the boiling water.
Cook manicotti according to package directions.
Usually takes about 8 minutes total.
Drain and rinse with cold water.
This stops them from cooking more.
Lay them flat on a towel.
Mix ricotta in a large bowl.
Add 1 cup mozzarella and Parmesan cheese.
Stir in the beaten egg gently.
Add parsley, salt, and pepper now.
Mix everything until well combined smoothly.
The filling should be creamy and thick.
Preheat your oven to 375°F now.
Spread 1 cup marinara in baking dish.
Use a spoon to fill each tube.
Pack the filling in carefully but firmly.
Place stuffed manicotti in the dish side-by-side.
They should fit snugly together nicely.
Pour remaining marinara over the manicotti evenly.
Make sure all pasta is covered completely.
Sprinkle remaining mozzarella on top generously.
Cover dish tightly with aluminum foil.
Bake covered for 25 minutes first.
Remove foil and bake 10 more minutes.
Cheese should be bubbly and golden brown.
Let it rest 5 minutes before serving.
This helps everything set up properly.