Preheat the oven to 180C/350F/gas mark 4
Use a 450g/1 lb loaf tin.
Combine the sour cream, buttermilk, vanilla, orange rind and melted butter. Sift together the dry ingredients, make a well in the centre and add the liquids. Mix lightly. Bake for 1 hour or until the cake shrinks away from the side of the tin. Leave to firm up in the tin for ten minutes. Turn out onto a wire rack to cool completely.
