For the sauce, put the Muscovado sugar, butter and syrup into a small saucepan and heat gently until dissolved. Share between 4 individual pudding bowls, tilting the bowls around so that the sauce coats the insides.
Sift the flour and salt into a mixing bowl. Add the sugar, TREX, unbeaten egg, milk and vanilla extract. Use a wooden spoon to beat the mixture together until smooth and creamy – this will only take 1-2 minutes. Stir in the dates, if using.
Share the mixture equally between the pudding bowls. Cover each one tightly with a piece of greased foil.
Place the bowls in a steamer, cover with the lid and steam steadily for 30-35 minutes, taking care that the steamer does not boil dry. Top up with boiling water if necessary. Carefully turn out the puddings and serve at once.