Heat 2 tablespoon olive oil in a large saucepan and add diced ingredients (2 small onions, 2 sticks celery, 2 small carrots). Sauté till softened but not browned.
Add 4½ lbs ground beef and cook on medium heat till the meat is brown, stirring occasionally and breaking up any clumps.
Pour in 5¼ cups Italian tomato sauce add 2 teaspoon salt and 1 teaspoon black pepper. Stir well, reduce heat to low, cover and cook for 30 minutes. Remove from heat and taste for seasoning. Tear half the basil leaves and stir into the sauce then cover and set aside till ready to use.
Combine the cheeses
In a medium bowl, whisk together 1 cup ricotta, 1 cup mozzarella and ¼ cut parmesan, cover and set aside. Stir in a tiny bit of milk if mixture is too dense.
Prepare the bechamel sauce
In a small saucepan heat 4 cups whole milk to almost boiling then pour into a heat proof measuring jug or bowl.
Melt ⅓ cup butter in a medium saucepan on medium heat and stir in ½ cup all-purpose flour to make a smooth roux . Slowly pour in a third of the warmed milk at a time stirring to make a smooth creamy sauce. Season with ½ teaspoon salt and ⅛ teaspoon nutmegmix and set aside.
Assemble and cook the lasagna
Preheat the oven to 180℃/350℉ and grease a large (20x30 cm or 9x13 inches) deep oven proof lasagna dish.
Spread a thin layer of meat sauce over the bottom of the pan and cover with 1 box lasagna sheets. Add another layer of meat sauce, then a layer of béchamel and top with the cheese mixture. Cover with lasagna sheets, ragù, béchamel, then the cheese mixture. Repeat layering till just below the top of the pan. The last layers should be meat sauce then béchamel.
Finish with 3 tablespoon parmesan (finely grated), 3 teaspoon butter dotted over the top and rest of the basil leaves.
Place in the middle of the preheated oven and bake for 35-40 minutes till the lasagna sheets are soft and the cheese is golden. Remove from the oven and leave to rest for a few minutes before slicing and serving.
Notes
Tip: use a potato masher to break up the ground beef.This recipe uses ready made lasagna sheets, either fresh or dried pasta sheets. * Fresh pasta sheets require less cooking time - use a fork to check noodles are tender after 30 minutes.Baking time: When baking the lasagna, follow the baking time on the lasagna sheets packaging so the lasagna sheets cook till fork tender.Storing: Wrap well in plastic wrap and store in the fridge for up to 3 days or freeze for up to 3 months. Defrost and remove plastic wrap before reheating, cover with parchment paper and heat in the oven at 180C/350F till warmed through.Make ahead: Assemble the lasagna, wrap and store in the fridge or freezer then bake at 180℃/350℉ for 30-40 minutes. To check the lasagna is cooked through, insert a knife into the lasagna noodles, they should be tender.