Simmer the prunes
in water to cover until soft, or soak overnight.
Drain, reserving 60ml/4 tbsp of the soaking liquid.
Stone and chop the prunes.
Combine the yeast
and the reserved prune liquid, stir and leave for 15
minutes to dissolve.
In a large bowl,
stir together the flours, bicarbonate of soda, salt
and pepper. Make a well in the centre.
Add the prunes,
butter, and buttermilk. Pour in the yeast mixture.
With a wooden spoon, stir from the centre, folding
in more flour with each turn, to obtain a rough
dough.
Transfer to a
floured surface and knead until smooth and elastic.
Return to the bowl, cover with a plastic bag and
leave to rise in a warm place until doubled in
volume, for about 1 1/2hours. Grease a baking
sheet
Punch down the
dough with your fist, then knead in the walnuts.
Shape the dough into a long, cylindrical loaf. Place
on the baking sheet, cover loosely, and leave to
rise in a warm place for 45 minutes. Preheat the
oven to 220C/425F/Gas 7.
With a sharp
knife, score the top. Brush with milk and bake for
15 minutes, Lower to 190C/375F/Gas 5 and bake for
35 minutes more, until the bottom sounds hollow.