2 large baking potatoes2 tablespoons butter1 onion, finely choppedKosher salt and freshly ground black pepper2 tablespoons light olive oilClean and scrub the potatoes well. Poke several holes in them to allow steam to escape. Place the potatoes on a small baking sheet and bake in a pre-heated, 420-degree oven, uncovered, until done, about 1 hour.Allow the potatoes to cool and refrigerate overnight.Peel the potatoes and cut into Z\c-inch dice. Melt the butter in a saute pan over medium-high heat and add the onion. Cook about 5 minutes. Season with salt and pepper.Transfer the onion to a small bowl. Add the oil to the skillet and heat on high until hot and almost smoking. Add the potatoes and turn the heat down to medium-high. Cook the potatoes, unstirred, until the crust is formed, about 5 minutes, then give a quick stir and, with a spatula, turn over the crusted potatoes.Season with salt and pepper and continue cooking until golden brown. Stir in the onion, season again with salt and pepper. Stir until the hash browns are heated through, about 3 minutes. Serve hot.Serves 6.