Preheat your oven to 350 degrees.
Add eggs to a large bowl and mix with milk.
Coat your muffin tin with olive oil or olive oil spray. I use the spray to get an even application.
Add your eggs to an easy to pour measuring cup and fill each cup hole to about 3/4 of the way full. If you're only adding cheese then fill a bit higher. Once in the oven your egg cups may start to rise a bit. They will fall once you remove them from the oven. So in order to have a full-sized egg cup you want to make sure the egg mix goes all the way to the top of the muffin tin holes once your toppings are in.
Add your other ingredients as you like. I added onion, ham, tomatoes and spinach, cheese and salt and pepper.
Add your muffin tin to the oven for about 20 minutes.
Once done, remove the muffin tin and pop your egg cups out. Let them cool for a few minutes and then enjoy!