Preheat oven to 400 degrees F (200 degrees C). Grease a 9×13 inch casserole dish.
Place potatoes in an even layer in greased dish. Sprinkle onion and bacon over potatoes, then dot with butter. Cover dish with foil.
Bake in preheated oven for 45 minutes. Remove foil and stir potatoes. Turn oven to broiler setting and allow potatoes to brown for approximately 5 minutes, until crispy. You may need to stir every minute or so to achieve even browning. Serve immediately.
