1. In a heavy 10- to 12-inch skillet, melt the butter in the olive oil over moderate heat. When the foam begins to subside, add the potatoes.
2. Turning them frequently with a metal spatula, cook for 15 minutes or until they are tender and golden brown.
3. Season with salt and a few grindings of pepper, then transfer the potatoes to a heated bowl or platter and serve at once, sprinkled with parsley if you like.
4. When fried potatoes accompany Iscas or Bife a Portuguesa, they are traditionally arranged in a symmetrical ring around the meat.
