For the beef: Heat the oven to 375°F/180°C. Roast the meat 15 minutes. Remove, and cool. Thinly slice with a sharp knife. Mix the oil, lemon zest and juice, and basil. Toss with the meat in a glass casserole. Season, and spread the mixture out, cover, and refrigerate all day or overnight, turning once or twice. Serve at room temperature.
For the potatoes: Bring a large pot of water to the boil. Salt it, as you would for pasta. Add the potatoes, and cook until tender when you test them with a fork. Drain. Toss in olive oil. Season with salt and pepper, and serve.
For the plate: Plate some beef and potatoes side by side on a plate and enjoy!