Wash, peel and slice potatoes into ⅛-inch rounds.
Heat a large cast iron or nonstick skillet over medium-high heat. Add oil, and heat until oil starts to ripple.
Evenly add potatoes to the skillet, and sprinkle onions over the top. Cover, and cook about 8 minutes. Remove lid, and add salt and pepper.
Flip potatoes; continue to cook, uncovered, about 10 more minutes, occasionally flipping and turning until potatoes are golden brown and tender.
Drain on paper towels, if desired. Serve immediately.