"Sauerbraten is a German specialty dish which usually involves marinating a tougher cut of beef in a red-wine vinegar marinade for up to 5 days, which produces a succulent taste experience unlike any other.
This is the Berlin version of this dish; as a native Berliner I enjoyed this dish as a child. Note the principal difference which provides the meat with a different tanginess and flavor - this recipe uses buttermilk as the chief marinade ingredient.
Note also that this recipe is best prepared in a Roemertopf, a lidded clay pot, which is soaked overnight in cold water before it is used"
Combine buttermilk with sliced onions, carrots, bay leaves, cloves, juniper berries, peppercorns. Allow beef to steep in this marinade for 2 days in a non-reactive container, covered with plastic wrap and stored in a dry, cool place. Turn the beef every 12 hours (once in the mornings and once in the evenings).
Drain the beef, reserving the marinade for later use. Pat beef dry. Cover top of roast with bacon slices and place roast in pre-watered clay pot (Roemertopf - see notes above). Distribute flaked butter evenly all over beef roast.
Pour marinade through a sieve into the clay pot (Roemertopf). Cover and roast in a slow oven for 2.5 hours.
Check roast for tenderness/doneness. If necessary, increase cooking time by half an hour.
Let roast stand 15 mins. before slicing on a bias. During this time, pour pot liquor into a saucepan. Add to it the red wine, correct seasonings with salt and pepper.
Bring mixture to a slow boil, add the crumbled gingersnaps to bind the gravy.
Serve immediately. Traditional accompaniments include either wide egg noodles tossed in butter or potato dumplings, and red cabbage.