In medium saucepan, combine the marinade ingredients: onions, red wine vinegar, water, brown sugar, kosher salt, cloves, juniper berries (optional), peppercorns, allspice, bay leaves.Bring to a boil, and then reduce heat and simmer for 10 minutes. Allow marinade to cool completely.
To marinate the roast, find a vessel that it fits it with just a little wiggle room and pour the cooled marinade over the top. Ideally, the roast should be completely submerged in marinade.Alternately, use a vacuum-sealer to seal the roast and marinade together. (This is our preferred method of marinating anything.)
Refrigerate prepared meat for 3 to 7 days, turning it in the marinade a couple times a day.
Oven-Braise the Roast
Preheat oven to 325°F [164 °C].Remove beef from marinade and use paper towels to pat it dry.Use a mesh strainer to remove the solids from the marinade. Discard the solids and reserve the strained marinade.
Preheat a dry Dutch oven on stovetop on HIGH for 5 minutes.Add enough vegetable oil to the Dutch oven to generously cover the bottom; about 3 tablespoons.
Brown prepared roast on all sides, about 2-3 minutes per side, until it is uniformly deep golden brown. This should take about 15 minutes.Remove browned roast from Dutch oven and place on a plate.
Reduce heat under Dutch oven to MEDIUM-HIGH.Add slices of onion to the hot pan and allow the rings to fry for about 3-4 minutes on each side, enough to soften. Stir as necessary.Place browned roast on top of onions.
Pour reserve marinade over roast. Cover Dutch oven with aluminum foil and place in oven.Do not use the Dutch oven lid; doing so concentrates too much heat, and cooks the meat too fast, resulting in a less-tender roast.Begin checking roast with an instant read meat thermometer at the 1-hour mark. (A 3½-4 pound marinated roast will take about 1¼ to 1¾ hours to cook to Medium-Rare.)
Remove the roast to a platter when the internal temperature reaches 130°F [55°C] for Medium Rare. (See NOTES below for additional cooking times/temperatures.)Loosely tent the roast with aluminum foil and allow to stand. The temperature will rise another 10-15 degrees after the roast has been removed from the oven.
Make Gingersnap Gravy
Strain the drippings from the bottom of the Dutch oven. Discard solids.Return the drippings to the Dutch oven.Place the Dutch oven back on the stovetop and heat over MEDUIM-LOW.Add honey and gingersnap crumbs to drippings and whisk until they completely dissolve.
Continue stirring until the gingersnap gravy begins to simmer and thicken. If the gravy seems too thick, add a little more water or some beef broth. If the gravy seems toe thin, add some more gingersnap crumbs.
Serve sliced sauerbraten with warm gravy.
Marinade: Some people prefer more marinade for their roast. If this is you, just double the marinade amounts when you make it.
Rare: Remove from oven at 125°F [52°C]. Temperature will rise to 135°F [57°C] in 10-15 minutes.
Medium Rare: Remove from oven at 130°F [55°C]. Temperature will rise to 140°F [60°C] in 10-15 minutes.
Medium: Remove from oven at 140°F [60°C]. Temperature will rise to 150°F [65°C] in 10-15 minutes.
Medium Well: Remove from oven at 145°F [63°C]. Temperature will rise to 155°F [68°C] in 10-15 minutes.
Well Done: For a fall-apart tender, well done roast, prepare the sauerbraten as outlined in the recipe, but instead of cooking it in the oven, cook it in a slow cooker on low for 6-8 hours.
Alternate Cooking Method - SLOW COOKERTo cook the roast in a slow cooker, transfer it to the slow cooker after you have fried the onions (Step 4, under "Oven-braise the Roast"), along with the fried onions and reserve marinade, and cook on LOW for 6-8 hours.