In another bowl, beat the butter, sugar and salt until light and fluffy. Beat in the eggs one at a time, waiting until each one is fully incorporated. Beat in the syrup and orange zest. Fold the flour and dates into the mixture, then pour into the pudding basin. Cover with parchment paper and foil. Trim off the excess, leaving a 4cm overhang. Allow a bit of slack in the centre so the pudding has space to rise. Tie string around the rim of the basin to secure the paper and foil. Fold the foil over the paper to stop the steam coming between the two.