Preheat the oven to 160C/325F/gas mark 3
Use a 450g/1 lb loaf tin.
Grease and line the loaf tin. Sift the flour, cinnamon, salt and baking powder into a mixing bowl, adding any residue of bran left in the sieve. Stir in the grated carrot and mix well.
In a large mixing bowl, cream the butter and sugar until pale and fluffy. Beat in the orange rind. Mix the sour cream into the creamed mixture, a little at a time. Fold in the flour mixture together with the walnuts, adding a little milk to give a soft, but not runny, consistency.
Spoon the mixture into the tin and level the top. Bake for about one hour until the loaf is risen, firm to the touch and just beginning to shrink from the sides of the tin. Leave to firm up in the tin for ten minutes then turn out onto a wire tray.
