Bring 2 litres of water to the boil, add salt and one lemon half.
Meanwhile, remove outside leaves from the artichokes and discard. Cut the artichokes in half and, using a spoon, remove the choke (fibrous inner centre) and discard.
Add artichokes to saucepan and simmer gently for 40 minutes. Drain and stand to cool slightly. Transfer to plates. Season with salt and pepper.
Whisk together water, oil, vinegar, juice of remaining lemon half, egg yolk and mustard.