Combine carrots, brown sugar, baking soda and shortening in a large bowl. Pour on boiling water and stir just to mix. Set aside until cool.
Beat eggs with a fork and add to cooled carrot mixture. Sift in baking powder, salt and all-purpose flour. Stir in whole wheat flour. Fold in walnuts. Pour into greased 8½ X 4½ X 2½″ loaf pan. Let stand 5 minutes.
Bake in moderate oven (350°) 1 hour. Remove from pan and cool on wire rack. Bread slices better if allowed to stand, wrapped in aluminum foil or plastic wrap, in a cold place overnight.