Put the chopped dates and bicarb into a heatproof bowl or jug, and pour over 300ml boiling water. Stir well then leave to cool to lukewarm (about 20 minutes).
Beat the softened butter with the sugar until light and fluffy and well combined.
Gradually add the egg, beating well after each addition.
Sift the flour with the baking powder and xanthan gum, then gently fold into the mixture in 3 batches using a large metal sppon.
Stir in the dates and their liquid (once cooled to lukewarm) to make a very thick batter-like mixture.
Spoon into the prepared ramekins - they should be no more than two thirds full, to allow space to rise in the oven. Set the ramekins on the baking sheet and bake for about 20 minutes until firm when pressed in the centre and a toothpick inserted in the middle comes out clean.
To make the sauce: melt the butter with the sugar over a low heat, then bring to the boil momentarily. Remove from the heat and whisk in the cream. Pour into a serving jug.
Leave the puddings to cool on a wire rack for 5 minutes then carefully turn out onto serving plates and serve hot with the sauce.