Potato Cake with Onion

Preparation Put oven rack in middle position and preheat oven to 375°F. Prick potatoes in several places with a fork. Bake potatoes in a large shallow baking pan until tender when pierced with a sharp knife, about 1 1/2 hours. Transfer to a rack to cool completely, then chill, uncovered, at least 8 hours. Peel potatoes, then shred with slicer into a bowl. Coarsely grate onion on large teardrop-shaped holes of a box grater, then wrap in 2 layers of paper towels and squeeze gently to remove excess moisture. Toss together potatoes, onion, salt, and pepper with a fork. Heat 2 tablespoons butter and 1 tablespoon oil in a 7- to 8-inch nonstick skillet over moderately high heat until foam subsides, then add potatoes, spreading them evenly and tamping them down with a rubber spatula. Reduce heat to moderate and cook Rösti until underside is golden brown, about 5 minutes. Wearing oven mitts, invert a flat plate over skillet, then invert Rösti onto plate. Add remaining 2 tablespoons butter and remaining tablespoon oil to skillet and heat until foam subsides, then slide Rösti (browned side up) back into skillet with rubber spatula. Cook until underside is golden brown, about 5 minutes. Transfer to a cutting board and cut into 6 wedges. Cooks' note:Whole baked potatoes can be chilled up to 2 days.

Preparation Put oven rack in middle position and preheat oven to 375°F. Prick potatoes in several places with a fork. Bake potatoes in a large shallow baking pan until tender when pierced with a sharp knife, about 1 1/2 hours. Transfer to a rack to cool completely, then chill, uncovered, at least 8 hours. Peel potatoes, then shred with slicer into a bowl. Coarsely grate onion on large teardrop-shaped holes of a box grater, then wrap in 2 layers of paper towels and squeeze gently to remove excess moisture. Toss together potatoes, onion, salt, and pepper with a fork. Heat 2 tablespoons butter and 1 tablespoon oil in a 7- to 8-inch nonstick skillet over moderately high heat until foam subsides, then add potatoes, spreading them evenly and tamping them down with a rubber spatula. Reduce heat to moderate and cook Rösti until underside is golden brown, about 5 minutes. Wearing oven mitts, invert a flat plate over skillet, then invert Rösti onto plate. Add remaining 2 tablespoons butter and remaining tablespoon oil to skillet and heat until foam subsides, then slide Rösti (browned side up) back into skillet with rubber spatula. Cook until underside is golden brown, about 5 minutes. Transfer to a cutting board and cut into 6 wedges. Cooks' note:Whole baked potatoes can be chilled up to 2 days.