This was originally a bread machine recipe that came from Allrecipes.com. I've tinkered with it just a bit. I converted it for sourdough and that version follows the yeasted one. Hope you like it.
Betty

Russian Black Bread

1 1/2 c water
2 t instant yeast
2 T cider vinegar
342.5 g bread flour
128 g dark rye flour
1 t salt
2 T soft butter
2 T molasses
1 T brown sugar
3 T dutch processed cocoa powder
1 t instant coffee granules
1 T caraway seed
1 t fennel seed

Mix water, yeast, flours until a shaggy mass is formed. Cover and autolyse for 30 minutes. Add everything but the seeds and mix on # 2 speed for 8 minutes or so. Check for window pane. I add the seeds at the end of the mix so they don't tear the gluten strands. Place in oiled bowl, cover and let double.
Punch(I hate that term, gently) down dough and shape. Proof until double. Bake at 375 for about 20-25 min and temp is 190-200.

Sourdough Version : Mix 1 1/2 c water, 2 T starter, 128 g dark rye and 228 g
bread flour, cover and let sit overnight. The next day add 115 g bread flour
and the rest of the ingredients EXCEPT the vinegar, yeast and seeds.
Mix on # 2 speed for 8 minutes or so, until window pane. Add seeds and mix until incorporated. Then follow as above