In a heavy medium skillet, heat 1 tablespoon olive oil over medium heat. Add onions and saute until softened and caramelized. Remove onions from skillet. Add remaining tablespoon oil to skillet and heat. Add diced potatoes in an even layer in the skillet, season with salt and pepper and cook until the potatoes begin to brown on the bottom, 6 to 7 minutes, shaking the pan occasionally to prevent sticking. Add onions back to skillet, press into a pancake. Season with salt and pepper.