Preheat the oven to 425 degrees . In a 10-inch, ovenproof nonstick skillet, cook the bacon over medium heat until crisp, about 5 minutes; drain on paper towels, then crumble. Transfer to a large bowl and toss with the potatoes and 2 tablespoons olive oil; season with salt and pepper.
Using the same skillet, add half of the onion and cook until softened, about 8 minutes; transfer to a bowl and wipe out the skillet. Add 1 tablespoon olive oil to the skillet and arrange one-third of the potato mixture evenly in the pan; sprinkle with half of the cooked onions. Repeat with another layer of potato mixture and cooked onions, then top with the remaining potato mixture. Cover with foil and cook over medium-high heat for 5 minutes. Transfer to the oven and bake until browned on the bottom, about 35 minutes. Let stand for 5 minutes, then loosen the edges using a spatula. Invert onto a platter; cut into wedges before serving.
Meanwhile, in another large skillet, cook the apples in 1 tablespoon olive oil until browned, about 10 minutes; transfer to a bowl. Add the remaining 1/2 tablespoon olive oil and onion to the skillet and cook until softened, about 3 minutes. Add the kale, lower the heat, cover and cook until tender, 8 to 10 minutes; season with salt and pepper. Serve with the potato cake, sour cream and apples.