Combine the onion, carrot, leek, garlic, raisins, salt, sugar, broth, 1 cup of wine, bay leaf, juniper berries, cloves, and peppercorns in a large pot, stirring to combine.
Bring the marinade to a simmer over medium heat, stirring occasionally, and cook for 10 minutes or until the vegetables are moderately tender.
Cool the marinade to room temperature.
Soak the roast in the marinade, then cover it and refrigerate for at least 2 days or a maximum of 5 days, turning it daily.
Remove the roast from the marinade, reserving the latter. Pat the roast dry with paper towels.
Heat the oil in a large pan over high heat.
Sear the roast for about 3 minutes per side until browned.
Bring the marinade to a simmer over medium heat.
Put the roast in the pot with the marinade and reduce the heat to low.
Cover the pot and cook the roast for 2 hours, flipping it after an hour.
30 to 40 minutes before the roast is done cooking, melt 3 tablespoons of butter over medium heat.
Stir the cabbage, remaining wine, and apple juice into the butter and bring the mixture to a simmer. Reduce the heat to low, cover, and continue cooking the cabbage for 20 to 30 minutes until tender. Season the cabbage with salt and pepper and keep it warm.
Fill a large pot ¾ full with water and bring it to a boil over high heat.
Cook the potatoes in the boiling water for 20 to 25 minutes or until tender, then drain them.
Melt the remaining butter in a pan over medium heat, then add the potatoes, stirring to coat them.
Sprinkle the potatoes with parsley, season them with salt and pepper, and keep them warm.
Take the cooked roast out of the pot and let it rest.
Strain the marinade, reserving the liquid.
Return the liquid to the pot and bring it to a simmer over medium heat.
Add the crushed gingersnaps to the sauce and continue to simmer it, stirring it frequently until the cookies break down and the sauce thickens to a gravy-like consistency.
Slice the roast approximately ¼-inch thick.
Serve the sauerbraten with the cabbage and potatoes on the side and the sauce on top.