Cut the butter into cubes and put it in a bowl with the dates, Chelsea Soft Brown Sugar and grated rind. Pour over the boiling water and stand for about 10 mins, stirring occasionally until the butter melts. Cool to room temperature.
Meanwhile, line the long sides and the bottom of a 7 cup (1 3/4 litre) capacity loaf tin, with a strip of baking paper. Butter or spray the ends of the tin.
Beat the egg until frothy. Stir the remaining ingredients together until well combined.
Tip the egg and the mixed dry ingredients on top of the cooled date mixture, then fold the three mixtures together, stirring only until everything is dampened, but not smooth. (If over mixed, the loaf will rise to a peak and be tough.)
Spoon into the prepared tin and bake for approximately 40 mins, or until a skewer inserted into the centre of the loaf comes out clean.