I grew up in Westfalia and miss eating "proper" Pumpernickel bread every once in a while. I finally hunted down a recipe that comes really close to what I want. And by the standards of this website, it turns out to quite easy to make. Given that it is an all-rye dough, it doesn't even require kneading. It's almost a quick-bread, if it wasn't for the long soaking times.
The only real challenge is the long baking time; in order to make that practical and economical, it makes sense to bake a big loaf -- and that requires both a big loaf pan and a big mixer. Or you could work in batches. As far as baking forms goes, you can always improvise. Due to the low temperatures, almost any ceramic, glass or metal container works, as long as it can be covered. And it is critical that all steam is trapped while baking.
I translated the German recipe to English and made a couple of minor adjustments for American ingredients. I also included links for some of the harder-to-find ingredients/tools. If you want to print the recipe, feel free to download the PDF  or HTML  version.
|350g||rye meal |
|200g||rye berries |
|350g||cracked rye |
|350g||rye meal |
|3 Tbsp||rolled rye |
Combine rye meal, water and sourdough culture and let rest at room temperature for 16 to 18 hours.
Combine rye berries with 200ml boiling water and let rest over night. The next day, add another 600ml of water, bring to a boil, and simmer at low heat for about one our. Discard excess water.
Combine cracked rye with water and let stand over night.
Combine all ingredients, except for the rolled rye and mix thoroughly . Then let rest for about 30 minutes.
Sprinkle 13" Pullman bread pan  with rolled rye and transfer dough to pan. Push dough to the side and sprinkle rolled rye on sides or loaf; then firmly pat down dough. Brush top of dough with water and sprinkle remaining rolled rye on top of loaf. Cover and let rest for another two to three hours.
Preheat oven to 300°F. Seal bread pan in an oven bag  and bake for 14 hours. After the first hour, reduce heat to 250°F.
Let rest inside of covered bread pan for at least 24 hours before serving.
Slice thinly. Can be frozen for up to six months.