Thinly slice raw potatoes and place in greased 9 by 13 inch pan.
Slice onions thin and place on top of potatoes.
In a small saucepan, heat butter, salts, and pepper until butter is melted, stir until creamy.
Drizzle over potatoes.
Cover with foil and bake at 425 for 45 minutes, or until potatoes are fork-tender. Sprinkle with cheese and parsley.
Bake uncovered for an additional 5 minutes or until cheese melts.