Prepare the Marinade: In a large Dutch oven, combine onion, carrots, leek, garlic, juniper berries, cloves, peppercorns, salt, and sugar.
Pour in red wine, vinegar, and beef broth. Add bay leaves, thyme, rosemary, and raisins.
Bring to a boil over medium-high heat, then reduce and simmer for 10 minutes.
Remove from heat and allow to cool completely.
Marinate the Meat: Place the beef in a glass or ceramic bowl. Pour the cooled marinade over the meat, ensuring it’s fully submerged.
Cover and refrigerate for at least 2-3 days, up to 10 days. Turn the meat once a day.
Sear & Braise: Remove beef from marinade and pat dry. Heat oil in a Dutch oven over high heat and sear the meat on all sides.
Strain the marinade, keeping the liquid and discarding solids.
Pour the strained marinade over the seared meat, bring to a boil, then cover and simmer over low heat for 2-2.5 hours.
Make the Gravy: Remove the beef and let it rest for 10 minutes. Strain the cooking liquid, return to the pot, and stir in crushed gingersnaps. Simmer for 10 minutes until thickened.
Serve: Slice the sauerbraten into thin slices and spoon the rich gravy over the meat. Serve with Rotkohl, Spaetzle, or potato dumplings.