Preheat oven to 325 degrees F (165 degrees C). Lightly grease a 9x13-inch baking dish.
Sprinkle cheese evenly in the bottom of the baking dish. In a large bowl, beat together eggs, milk, mustard powder, salt and pepper. Pour egg mixture on top of cheese.
Bake in preheated oven for 40 minutes or until firm. Let cool slightly before cutting into squares to serve.
