Heat a large skillet with extra-virgin olive oil and butter over medium-high heat. Add onions and let soften 2 to 3 minutes. Add potatoes, season with salt and pepper and cook 20 minutes, turning occasionally, until brown and crispy. Season with a little freshly grated nutmeg, to taste, and add cheese. Turn the potatoes and onions with cheese to melt the crumbles and crisp the cheese a bit, about 1 minute. Transfer to serving dish.
Recipe courtesy of Rachael Ray, 2007