Boil water with a bit of salt. Throw fettuccine in and stir so they don't stick. I usually add a tsp of olive oil or butter to the boiling water to prevent the pasta from sticking. Boil for about half of the time indicated in the box, usually 6-8 minutes instead of the regular 12-14 minutes.
Turn oven on at 380 degrees Fahrenheit (about 190 degrees Celsius) so it can pre-heat.
Melt about 1 tbsp of the butter and coat the bottom of the baking dish.
Once the pasta has cooked for 6-8 minutes, drain the water and pour pasta in the baking dish. Arrange so it fills the dish evenly. I used a 9x13 baking dish.
Crumble the feta cheese and spread with a fork in between pasta and over. Cube the butter and repeat. Pasta is still warm enough that butter will start melting slowly.
Whisk eggs and then add the milk, keep whisking for a minute or so. Then pour this mix over the pasta. Use the fork to move the pasta slowly so the egg/milk sauce can set in evenly.
Bake for about 30 minutes. If the top is getting too crispy, lower the dish to the bottom rack or cover with an aluminum foil. I personally like a little bit of crisp on top so I don't cover it.
Add bechamel sauce (instructions not included) if you don't like a crispy top.
Sprinkle with parmesan cheese about 2 minutes before you'll turn oven off.
Once casserole is baked, let it cool for about 15 minutes before you cut it in square pieces. Serve warm!
Notes
I would like to add a note on the eggs. It's preferred to use eggs from pasture raised chickens for this dish. Those eggs have a bright orange egg yolk compared to an opaque yellow from regular eggs. The deep orange color gives a more appealing look to this casserole.
I use a lot of feta cheese so I add very little salt to this dish since feta cheese is already very salty. Adjust salt accordingly.