Totally not hard to make at all, yet it comes off as a special occasion/for entertaining meal. I use it as such b/c of how easy it is to do (it can be accommodated to be more or less difficult) and it leaves us gobs more time to do other things. I have a few altered recipes where I use boiled noodles and roll the filling into individual noodles, but that is a little time consuming. I actually know people who are afraid to make their own homemade red sauce let alone attempt a lasagna. I praise my good Italian upbringing for my "it's too easy" mindset. Depending on how you tailor it it can be really inexpensive, too. We have the privilege of Commissary shopping, so even pre-shredded bags of cheese are around $2.00 for plenty.
You can start a day ahead if you wish, which I often do. I will make a huge batch of sauce and use it for two or three meals (and lasagna and pasta make great leftovers for work lunches or leftover nights). I can't understand why people insist on using store bought jarred sauce, b/c it doesn't really take that much more time to make and it is tons cheaper. If you grow and can your own tomatoes it is cheaper still (which I am hoping to do this fall).
In a large, deep pre-heated skillet (like a big cast iron or stainless) rim the pan about three times w/ EVOO. I like to toss two bay leaves into the heating oil. You can either smash and mince about 2-3 cloves of garlic or use the pre-minced stuff. Finely chop 1/3-1/2 of an onion (I use white or shallots, but Maui Sweets, Walla Wallas, Spanish Yellows all work just as well) and toss into the hot oil. If you are using fresh garlic put them in together so that you don't scorch the garlic. Cook the onions down nicely. This is a great time to grate in some carrot or some zucchini, which add nice natural sugars to cut the acidity instead of resorting to using white sugar (which I consider a Mortal Sin). It's also a nice sneaky way to get extra vegetables in there.
If you want a meat sauce add the meat now. For lasagna, if I am making a meat one, I use a tube of port sausage and 1/4 - 1/2 pound ground beef. It makes the sauce thick and hearty. I leave it out a lot too and will fill the lasagna w/ either lots of mushrooms or thawed, rinsed chopped spinach. Thin slices of vegetable, like peppers, zucchini, and yellow squash layered in make a great pie as well.
When the onions are cooked down or the meat fully browned is the time to add a large can of pureed tomatoes (a 29-32 ounce can) or crushed tomatoes. This will cook the meat bits off of the bottom of the pan. If you like chunky sauce add a can of diced tomatoes now and simmer. Season after every step w/ salt, pepper and your choice of herbs. The Guy is a huge fan of oregano, and I like a mixture of rosemary, crushed red pepper sage and thyme (I also sometimes make a "Scarborough Fair" sauce...LOL). Something I fell in love w/ here in Korea is gochujang and I will drop a spoonful of that into the simmering sauce. It's great and you should not be afraid of it.
Turn this to simmer w/ a lid on it and fagettaboutit!
In a mixing bowl combine a carton of ricotta cheese w/ a large handful of mozzarella and a smaller handful of parmesan. Most recipes also call for an egg, but I am anti egg and have never noticed that it makes a difference to anything I have had elsewhere. Smash this together w/ a spoon. This is something else you can do a day before and refrigerate if you want.
The assembly is the last part, and you should preheat your oven to about 375 (which is just under the 200 mark on my Korean oven! Yay!) while you assemble. Assembly is different depending on the pan you use, and normally I use a DeMarle baking form, which you layer upside down (mozzarella cheese, sauce, noodles; ricotta mixture, sauce, noodles; ricotta mixture, mozzarella, sauce, noodles; ricotta mixture, noodles, sauce) and turn out onto a plate, but we only have our Pyrex that we had to get since our stuff isn't here yet.
I have fallen in love w/ the no boil noodles which are flat like the hand made traditional ones, but use whatever you have available. In a glass dish layer it so: sauce, noodles, 1/3 ricotta mixture, a sprinkling of mozzarella, sauce; noodles, 1/3 ricotta mixture, sauce; noodles, last of ricotta mixture, sauce; noodles, sauce, mozzarella (and throw some parm on there for good measure! CHEESE!). If you don't have foil to cover this for baking leave the cheese off until the last 15 minutes or so of baking, then broil for about 2-3 at the end. If you do, slap that puppy in for about 45-50 minutes covered, and remove foil and broil for 2-3 minutes.
This is one that I didn't have enough sauce for and just used a can of diced tomatoes on top, seasoned them and baked uncovered for about 30 minutes before adding the cheese.
The bay leaf! You know what that means!
All pretty and browned!