Crisp Bacon. If you haven't already, crisp the bacon and crumble or dice it into small pieces.
Layer. Lightly grease a 9x9 baking dish (I like a ceramic or glass pan for this!) Add thawed frozen potatoes, season with a pinch of salt & pepper, and top with grated Pepper Jack cheese, grated cheddar cheese, and green onions.
Mix Up The Eggs. In a medium bowl, combine eggs, milk, and 1/2 teaspoon salt and 1/4 teaspoon black pepper. Whisk until the egg mixture is smooth and the egg whites are evenly mixed in.
Assemble. Sprinkle cooked bacon on top of the potatoes & cheese, then pour the egg mixture over everything.
Cover & Chill. If you're making this casserole the night before, cover the pan with plastic wrap or aluminum foil and chill in the refrigerator overnight, up to 10 hours in advance.
Preheat The Oven. Remove the casserole from the fridge while you preheat the oven to 350 degrees F.
Bake 40-45 minutes, or until the center of the casserole is just set. Garnish with fresh cilantro and another sprinkle of black pepper. Allow the casserole to cool 15 minutes before cutting and serving (this will help the eggs set up!)
Serve & Store. Enjoy warm with hot sauce and a side of fresh fruit & your favorite muffins, waffles, pancakes or cinnamon rolls! Keep leftovers covered in the pan or transfer to an airtight container. Leftover egg casserole will keep 3-4 days in the fridge.