In a large mixing bowl, combine red wine vinegar, red wine (use grape juice if available), bay leaves, black pepper, cloves, juniper berries (if unavailable, use extra black pepper), sliced onions, sliced carrots, and sugar to create the marinade.

Place the beef roast in a large non-reactive container or heavy-duty plastic bag, pour the marinade over it, ensuring the meat is fully submerged. Cover and refrigerate for 2-3 days, turning once daily.

Remove the beef from marinade (reserve marinade), pat dry with paper towels. Season with salt and black pepper.

Heat vegetable oil in a large dutch oven over medium-high heat. Brown the beef on all sides, about 10-12 minutes total. Remove and set aside.

In the same pot, add sliced onions and carrots from the marinade, sauté for 5 minutes until softened.

Return beef to pot, pour in the reserved marinade with all spices, add beef broth to nearly cover the meat. Bring to a boil.

Reduce heat to low, cover tightly, and simmer for 2.5-3 hours until meat is fork-tender, turning occasionally.

While meat cooks, prepare spätzle: Mix flour, eggs, milk, and salt in a bowl until smooth batter forms. Let rest 10 minutes.

Bring a large pot of salted water to boil. Press batter through a spätzle maker or colander into boiling water. Cook until noodles float, about 2-3 minutes. Drain and toss with butter.

Remove beef from pot, tent with foil to keep warm. Strain cooking liquid, discard solids. Return liquid to pot and simmer to reduce by half, about 15 minutes, creating a rich gravy.

Slice beef against the grain, arrange on serving platter with spätzle and braised vegetables. Pour gravy over top and serve immediately.