An Italian classic.
Recipe

Cook the sauce.

Pasta, sheets or lasagne strips, dried or fresh, 1 pound or so
You don’t need to boil the pasta; as long as your sauce is liquid enough, it will cook in the oven.

A large baking dish, oven-safe casserole, or a pair or loaf pans

Pre-heat your oven to medium (350 degrees)

Ricotta cheese, 2 pounds

Eggs, 2

Nutmeg, if available.

Mix the contents of the eggs into the ricotta. Grate a bunch of nutmeg over it.

Mozarella cheese, 1 pound

Parmesan cheese, around 1 cup

Slice or shred the Mozzarella, and coarsely grate the Parmesan.

Scoop several spoonfuls of tomato sauce into the bottom of the baking dish, then a layer of pasta, then spread out a couple spoonfuls of ricotta, scatter in some mozarella and parmesan, then another pasta layer, then back to more tomato, continuing until you’ve used up all your ingredients.
Try to end up with a top layer of tomato, with the last of the parmesan scattered on top of that.
It doesn’t really matter what order the internal layers come in, but do make sure you don’t ever have two adjacent sheets of pasta with nothing between them.

Cook in oven for around half an hour, or until it’s hot all the way through and the pasta in the middle is cooked enough that you can poke a fork through it.
Set aside to cool for several minutes before serving, to allow it to set.