Potatoes and onions are a ho-hum combination, but in this recipe, inspired by classic French pommes de terre à la Lyonnaise, the humble ingredients become a fantastic dish. The secret: brown the potatoes and onions in butter so they take on a wonderful nutty flavor. This rustic side pairs deliciously with everything from seafood to meat, or simply serve them with eggs. To jump-start the cooking process, we partially cook the potatoes in the microwave, then finish them in the skillet. Be sure to rinse them well before microwaving; this removes some of the excess starch that will cause the slices to stick together.