Impress with this crowd-pleasingly meaty main. Juicy steak is grilled to perfection, covered in a creamy pepper sauce and served alongside sauteed potatoes and spinach. Preheat the oven to Gas 5, 200°C, fan 180°C. Cook the diced potato in a large saucepan of salted, boiling water for 10 minutes until soft. Drain and leave to cool. Transfer to a roasting tray and drizzle with 2 tablespoons of the groundnut oil. Season well and roast for 20 minutes, until golden and crisp. Place 2 sturdy frying pans over a high heat. Rub the steaks with the remaining tablespoon of groundnut oil and season well. Add 2 steaks to each frying pan and sear for 1 and a half minutes before turning them over and cooking for 2 minutes more, until well-browned on the outside and medium-rare inside. For medium to well-done, add 30-45 seconds to the cooking time on each side; for rare steaks, subtract 30 seconds from the cooking time on each side. When cooked to your liking, remove the steaks to a plate and leave to rest for 3 minutes, covered loosely with aluminium foil. Meanwhile, combine all the ingredients for the sauce in a small saucepan and bring to a simmer. Remove from the heat, stir in the lemon juice and the juices that have collected on the plate from the rested steaks. Adjust the seasoning to taste. Arrange some of the spinach leaves on plates and sit the steaks on top. Spoon the sauce over and arrange the potatoes alongside. Garnish with a few chives before serving.