Melt butter in a flat pan of 8-inch diameter. Lightly sauté onions. Spread the potatoes over onions and sprinkle salt and pepper to taste. Gently toss the potatoes to coat the butter. Flatten the potatoes slightly and spread evenly on the skillet. Let cook undisturbed on medium heat for 5 minutes or until the bottom becomes brown. Flip the hash-brown to cook both sides evenly.

Serve immediately.