Begin by preparing the potatoes. Remove the skins and cut them into either quarter-inch-thick slices or small, evenly sized cubes for faster and more uniform cooking. Place them in a bowl of cold water and allow them to soak for 15 to 30 minutes. This draws out some of the surface starch, promoting a crisp finish during frying.

Once soaked, thoroughly drain the potatoes and blot them dry using paper towels. Ensuring the potatoes are as dry as possible helps them brown evenly and develop a crisp surface in the skillet.

Place a heavy-bottomed or cast iron skillet over medium-high heat. Pour in the cooking oil and, if using, add the butter. Allow the fats to heat until shimmering and hot, with the butter fully melted.

Distribute the potatoes evenly in the pan, ensuring they’re in a single layer. Let them sear undisturbed for approximately 5 to 6 minutes, allowing a crust to form. Flip and continue cooking on the other side for an additional 5 minutes, or until golden and crispy.

Incorporate the thinly sliced onions into the pan with the potatoes. Continue sautéing the mixture, stirring every few minutes, until the onions become soft and caramelized and the potatoes are fully cooked through and browned. This should take 10 to 15 minutes.

Finish by seasoning the dish with salt, pepper, and garlic powder. For additional depth of flavor, consider adding a light sprinkle of paprika, a hint of cayenne, or freshly chopped herbs. Serve immediately while hot for the best texture.