First make the soaker. Mix 2 cups of whole wheat flour, the bran, salt, vinegar and 1 cup water together in a bowl until all of the flour is hydrated. It doesn't need kneading, just mixing together. I found that I needed a little more water and this can change from flour to flour. The soaker should be somewhat like a slightly sticky bread dough in consistency. Cover the bowl loosely with plastic wrap and leave at room temperature for about 8 to 12 hours (overnight is good).
The next morning, add the remaining whole wheat flour, the yeast, the honey, butter, honey and milk powder to the soaker. Add a little more water if necessary and knead the dough well until the dough is elastic but no longer sticky. Put the dough in a lightly greased bowl, cover and leave to rise for about 1 1/2 hours.
Turn the dough out on a lightly floured surface and press it out into a big oval. Sprinkle half the chopped nuts and dates over the dough and fold the dough oval in half. Sprinkle the remaining walnuts and dates over this and fold again. Press out again into an oval shape and roll the dough, jelly roll style. Pinch the seam closed and tuck the sides down neatly.
Place the dough in an oiled loaf tin dusted with bran (8 1/2" x 4 1/2"), loosely cover and let it rise for about 45 minutes to an hour. Check if it's ready to bake by pressing a floured finger in the dough, it the dent springs back, leave it to rise longer, if the dent doesn't disappear, it's ready to bake.
Brush the top of the dough with water and sprinkle some bran over it. Bake the bread at 200C (400F) on a stone or metal tray pre-heated in the oven for about 30 to 45 minutes. If the top browns too quickly cover with aluminium foil, and bake till the bread is done and sounds hollow when tapped.
When done unmould the bread gently and let it cool completely before slicing it.