Boil water in your large pot.
Add salt to the boiling water.
Cook manicotti shells for 8 minutes.
They should be slightly undercooked.
Drain and set aside to cool.
Brown ground beef in a skillet.
Add Italian sausage and ground pork.
Cook until no pink remains.
Drain excess fat completely.
Add minced garlic and Italian seasoning.
Stir well and let cool slightly.
Combine ricotta cheese in mixing bowl.
Add 1 cup mozzarella cheese.
Mix in Parmesan cheese and egg.
Add salt and pepper to taste.
Stir in half the cooked meat.
Mix until everything combines well.
Preheat your oven to 350°F.
Spread 1 cup marinara in baking dish.
Carefully fill each manicotti shell.
Use a spoon or piping bag.
Place stuffed shells in the dish.
Pour remaining marinara over the shells.
Sprinkle remaining mozzarella on top.
Add the rest of cooked meat.
Cover dish with aluminum foil tightly.
Bake covered for 25 minutes.
Remove foil and bake 10 more minutes.
Cheese should be bubbly and golden.
Let it rest 5 minutes before serving.