Heat the vegetable oil in a large skillet at medium-high heat.
Add the potatoes and use your spatula to make sure the potatoes are fairly evenly coated with oil.
Lightly grease a 13 X 9 baking pan.
Let the potatoes cook about 5-7 minutes. Check the bottom. If the bottom of the potatoes is brown, turn the potatoes. Leave the potatoes to cook another 5-7 minutes, and then recheck them. Make sure you keep the turning to a minimum.
Beat the 12 eggs in a large bowl. Add the milk, salt, and pepper and beat together.
When the potatoes have been thoroughly cooked, remove them from the pan and arrange them evenly on the bottom of the 13 X 9 baking pan.
Pour the egg mixture over the top.
Add any of the optional ingredients.
Cover with the cheese.
Bake at 350 degrees F for 40 minutes or until a knife inserted in the center comes out clean.