In a large mixing bowl, combine the red wine, red wine vinegar, chopped onion, chopped carrot, chopped celery, bay leaves, peppercorns, cloves, juniper berries, allspice berries, and brown sugar.

Place the beef roast in a Dutch oven and pour the marinade over it. Cover and refrigerate for at least 24 hours, turning the roast occasionally.

Preheat the oven to 325°F (165°C). Remove the beef roast from the marinade and pat dry with paper towels. Strain the marinade and reserve the liquid. In a Dutch oven, melt the butter over medium heat. Add the beef roast and brown on all sides. Remove the beef roast from the Dutch oven and set aside.

In the same Dutch oven, add the reserved marinade liquid and bring to a boil. Reduce heat to low and simmer for 10 minutes. In a blender, blend the gingersnap cookies and flour until fine. Slowly whisk the gingersnap mixture into the simmering liquid until thickened.

Return the beef roast to the Dutch oven and pour the sauce over it. Cover and transfer to the preheated oven. Braise for 2 to 3 hours, or until the beef is tender.

Remove the beef roast from the Dutch oven and let it rest for 10 minutes. Slice the beef roast and serve with the sauce.