1) In a large cast iron skillet over medium heat, add onions, turkey, and garlic with the oil or butter. It is important to have cast iron for this recipe because we are going to transfer it to the oven. Preheat oven to 375 degrees F.
2) While those are starting to cook, crack your 8 eggs into a bowl and whisk together with your milk. Also chop up any and all herbs you wish to add and grate that cheese!
3) Then pour all of your egg mixture in your skillet. It should pretty much cover all of your fillings. Then sprinkle your herbs and cheese on top!
4) Turn heat down to low and cook for five minutes without touching it.
5) Transfer your jiggly thing to the oven for at least 15 minutes. Depending on how many eggs you use, and how large your cast iron skillet is, you might need a bit longer. You want the cheese to be bubbly and the egg to be firm.
6) If you have a well seasoned cast iron skillet then you should be able to just slide out the entire frittata onto a baking sheet, pizza stone, or large serving dish. Just work a spatula under one side, go slowly, and it should just slide right out.
Slice and serve!