To make the dressing, mix all the ingredients together in a small bowl. Spoon ¼ cup of the dressing over the steaks and marinate for 20 minutes in a cool place. Reserve the remaining dressing.
Put the rice in a saucepan with the stock and lime leaves. Bring to the boil, then cover and simmer for 10 minutes, or according to the packet instructions, until tender.
Meanwhile, pat the steaks dry with paper towels. Heat a cast-iron chargrill pan or non-stick frying pan over a high heat until hot. Brush with oil, then add the steaks and cook for 2½ minutes on each side for rare meat. Cook for longer if you prefer it medium or well-done. Remove the steaks from the pan and leave to rest for a few minutes.
Place the papayas, cucumber, mint, coriander and red onion in a bowl. Add all but 1½ tablespoons of the remaining dressing and toss gently to mix.
Drain the rice well and divide among four plates. Arrange the lettuce leaves on the plates and top with the papaya salad. Slice the beef into strips, arrange on top of the salad and spoon the remaining dressing over the top. Sprinkle with the peanuts, then serve at room temperature.
• If you prefer, you can use the grated zest of 1 lime instead of kaffir lime leaves. * • For a Thai red curry and orange dressing, combine 1½ tablespoons vegetable oil, 1½ tablespoons light soy sauce, 1 tablespoon light brown sugar, 1 teaspoon Thai red curry paste, ½ teaspoon grated orange zest and 2 tablespoons orange juice.