Preheat oven to 350 degrees. Grease a 10x12 inch casserole dish.
Bring a pot of salted water to a boil. Cook the sliced potatoes for about 10 minutes. Drain, and cool.
Whisk together the eggs, cream, salt and pepper. Stir in the onions, manchego, chorizo, parsley, and potatoes.
Pour into the baking dish. Bake about 45 minutes, or until eggs are set.
Cool slightly. Cut into 1 1/2 inch squares.