Preheat oven to 325 degrees.
Crack eggs in a large mixing bowl. Break egg yolks (with whisk) then whisk together. Add half and half, salt and pepper and mix.
Stir in cheese and mix-ins (or if using cheese only you can sprinkle over the top after pouring eggs into pan).
Spray a rimmed 18 by 13 by 1-inch baking sheet very well with non-stick cooking spray.
Pour egg mixture into pan, carefully transfer to oven (tip: it's helpful to do this step on the countertop near oven so you don't have to walk far so the eggs don't spill out).
Bake in preheated oven until eggs are just barely cooked through in the center, about 20 to 25 minutes.
