First, in a large mixing bowl combine the flour, baking powder and sugar, then rub the butter into the dry ingredients until the mixture is coarsely crumbled.
Add the grated lemon and orange rinds, the mixed spice and dried fruit.
Stir all these together and add the milk a little at a time, followed by the vinegar.
Stir until all the ingredients are evenly distributed, then stir in the marmalade – and you should have a good dropping consistency (so that if you tap a spoonful of the mixture on the side of the bowl, it drops off easily – you can adjust this with a touch more milk if necessary).
Now spread the mixture evenly in the prepared tin using the back of a tablespoon, and sprinkle the top with the demerara sugar.
Bake on a lower shelf so the top of the tin is aligned with the centre of the oven for 1¼ hours or until the cake feels firm in the centre. (After the cake has had 50 minutes, cover loosely with a piece of foil to prevent the sugar burning.)
Leave to cool in the tin for 10 minutes before turning out onto a wire cooling rack.
Store in its liner in an airtight tin – it does improve with keeping.
Pre-heat the oven to 180°, gas mark 4
Equipment: You will need a Delia Online Loaf Tin (or a standard 2lb loaf tin), lined with a 2lb traditional loaf tin liner.