In a large bowl, combine chopped onions, garlic, red wine, and wine vinegar. Place the rabbit in this mixture, cover, and let it marinate in the refrigerator for at least 4 hours, preferably overnight.

Heat oil in a large Dutch oven over medium-high heat. Remove the rabbit from the marinade and pat dry with paper towels. Brown the rabbit pieces on all sides, about 5 minutes per side, then set aside.

In the same pot, add the onions and garlic from the marinade. Sauté until translucent, about 3-5 minutes.

Pour in the remaining marinade and bring to a simmer. Scrape up any browned bits from the bottom of the pot to add more flavor.

Add the rabbit back to the pot along with chicken stock and thyme. Bring to a boil, then reduce heat to low and cover. Simmer for about 1.5 to 2 hours, or until the meat is tender and easily pulls away from the bone.

Once the rabbit is cooked, remove it from the pot. Dissolve the flour in a little water and stir it into the sauce. Cook for an additional 5-10 minutes until the sauce thickens.

Return the rabbit to the pot to coat it in the sauce. Serve hot, garnished with fresh thyme if desired.