4 fillet steaks, about 150 g each
1 onion, chopped
1 teaspoon parsley, chopped
1 tablespoon unsalted butter
1 tablespoon olive oil
1 tablespoon lemon juice
a pinch of salt
a pinch of pepper

Preheat oven to 200°C (400°F). Rinse the meat, pat dry and trim any fat or sinew. 
Mix the olive oil, lemon juice, onion, parsley, salt and pepper together in a bowl. Place the fillets in a large pan, pour the mixture over and roast the meat on both sides, on high heat. Cook 3 minutes on each side (for rare cooked meat, 4 minutes for medium and 5 minutes for well done). Use forceps rather than fork, not to drill the meat so that it'll keep its juice. Remove from the pan, place the meat in a baking tray coated with the butter and cover with a sheet of foil. Cook in the oven (for 35 minutes for rare cooked meet, 45 minutes for medium and 55 minutes for well done). Open the foil during the last 15 minutes of the cooking time. Cut the beef in thick slices and serve warm. Combine with green salad of your choice.