- Place beef rump roast, onions, vinegar, water, 1 tablespoon salt, 1 tablespoon black pepper, sugar, cloves, and bay leaves in a large pot. Cover and refrigerate for 2 to 3 days, turning meat daily. Remove meat from marinade and pat dry with paper towels, reserving marinade.
- Season flour to taste with salt and black pepper in a large bowl. Sprinkle flour mixture over beef.
- Heat vegetable oil in a large Dutch oven or pot over medium heat; cook beef until brown on all sides, about 10 minutes. Pour reserved marinade over beef, cover, and reduce heat to medium-low. Simmer until beef is tender, 3 1/2 to 4 hours. Remove beef to a platter and slice.
- Strain solids from remaining liquid and continue cooking over medium heat. Add gingersnap cookies and simmer until gravy is thickened about 10 minutes. Serve gravy over sliced beef.