In a large bowl, combine the red wine, red wine vinegar, chopped onion, minced garlic, bay leaves, peppercorns, cloves, thyme, sugar, and a pinch of salt.
Mix well and refrigerate for at least 24 hours, allowing the flavors to meld.
Place the beef roast in a large resealable plastic bag or covered container. Pour the marinade over the roast.
Seal the bag or container and refrigerate for 3 to 5 days, turning occasionally to ensure even marinating.
Remove the beef from the marinade and pat dry with paper towels. Discard the marinade.
Heat the vegetable oil in a large pot or Dutch oven over medium-high heat.
Brown the beef on all sides until well-seared, about 4-5 minutes per side. Remove the beef and set aside.
In the same pot, add a bit more oil if needed and sauté the remaining chopped onion until softened and golden.
Sprinkle the flour over the onions and stir to combine, cooking for 1-2 minutes.
Gradually add the beef broth, stirring to create a smooth sauce.
Return the beef to the pot along with any juices that have collected. If using, add raisins and crushed gingersnaps.
Bring the sauce to a simmer. Cover the pot and cook the beef for about 2.5 to 3 hours, or until the meat is tender and easily shreds with a fork. Turn the beef occasionally to ensure even cooking.
Remove the beef from the pot and let it rest for a few minutes before slicing.
If desired, thicken the sauce further by simmering it uncovered or by adding more crushed gingersnaps or bread crumbs.
Adjust seasoning with salt and black pepper to taste.
Slice the Sauerbraten and serve with the sauce poured over the top.
Sauerbraten is traditionally served with red cabbage, potato dumplings, or boiled potatoes.
Enjoy your meal!