Preheat the oven to 350℉.
Crisp the bacon over low heat in a 10 inch cast iron pan, then remove to a paper-towel lined plate. Pour off all but thin layer of bacon grease, reserving it for future use. Chop the bacon once cool.
4 strips bacon
In same cast iron pan, saute the leek until it has softened and lightly browned. Then add the garlic and kale and cook until it is lightly wilted. Remove the pan from the heat.
1 leek, 1 bunch kale, 2 cloves garlic
In a medium bowl, lightly beat 6 of the 8 eggs and then combine with the chopped bacon, kale, leek, cheeses, salt and pepper.
8 eggs, 1 cup cheddar cheese, ¼ cup Parmesan, 1 teaspoon salt, ¼ teaspoon black pepper
In a small bowl, crack remaining 2 eggs and beat lightly. These will form the base of the frittata.
If necessary, add back a bit of bacon fat to the cast iron pan and cook the 2 eggs as you would an omelet, tilting the pan so that all the egg is just set.
Remove the pan from heat, add the remaining eggs and ingredients, and bake for 20 to 25 minutes until the top is set. If you want, you can brown the top under the broiler for a minute or two.