Bring a large pan of water to the boil. Put the artichokes in the boiling water – sit a colander on top of the pan to submerge them – and simmer for 30–40 minutes. The leaves should break away easily when the artichoke is cooked. Remove the artichokes and drain upside down to release all the water.
Meanwhile, make the vinaigrette: place the mustard, sugar, seasoning, lemon juice and vin