Sift the flour, bicarbonate of soda, spices and salt into a bowl and stir in the sugar, suet, dried fruits, and the grated carrot or apple.
Mix the black treacle with the egg and some of the buttermilk and mix into the dry ingredients to give soft mixture with a cake-like dropping consistency.
Dip a large piece of muslin, an old pillowcase, a pudding cloth or a tea towel into boiling water, remove it and squeeze out the excess water. Lay it out on a surface and sprinkle a 30cm/12in circle in the centre with the 25g/1oz of flour and the 1 tbsp of caster sugar. Spoon pudding mixture on top and tie securely with string, leaving a little room for the pudding to expand.
Rest a large heatproof trivet or container in the base of a large pan so that the pudding is not in direct contact with the heat. Place the pudding on the trivet/container, knotted side up. Pour in enough water almost to cover the pudding, cover with a tight-fitting lid and simmer gently for 3-4 hours. Take a peek every now and then and then to check the water level and top it up if necessary.
Preheat the oven to 180C/350F/Gas 4. Lift the pudding out of the pan and dip it briefly in a bowl of cold water (to ensure that the outside of the pudding does not stick to an ovenproof serving plate). Then remove remove the cloth and place the pudding on an ovenproof dish/plate. Slide it into the oven and leave it for 15 minutes until the outside of the pudding has dried off.
Serve in chunky wedges with scoops of clotted cream and perhaps a small glass of whisky.