Place potatoes, unpeeled, in a saucepan with water to cover and salt.
Cook potatoes until tender, about 20 minutes. Drain and let cool. When cool enough to handle, peel them. Cut potatoes into 1/4-inch rounds.
Heat the oil in a nonstick skillet large enough to hold potatoes in one layer. When oil is hot, add potatoes. Cook over high heat, shaking skillet and stirring gently, until lightly browned. Turn potatoes with a spatula. Cook for a few minutes more until light brown.
Drain excess fat from skillet and add onion. Cook a few minutes until onion is lightly browned. Add butter, garlic, salt and pepper and blend well.