Pour vinegar and 1/4 cup olive oil in a shallow, sealable dish.
Add 3 cloves minced garlic. Stir to combine.
Place flank steak in marinade and turn to coat fully.
Seal dish and place in refrigerator overnight to marinate.
When ready to cook, remove flank steak from marinade, allowing excess to drip off. Discard used marinade.
Season flank steak with salt and pepper.
Pour 2 tablespoons olive oil into a large skillet or Dutch oven. Place over medium heat.
When oil is hot and shimmering, sear steak on both sides until browned, about 2 - 3 minutes per side. Remove and set aside.
In the same pan, reduce heat to medium. Add onion and bell peppers. Sauté until soft, about 6 - 8 minutes.
Add 3 cloves garlic. Cook 1 minute more.
Stir in cumin, oregano and paprika.
Pour in crushed tomatoes, beef broth and white wine.
Add bay leaf.
Return steak to the pan, nestling it into the sauce. Cover and simmer on low heat for 1 1/2 to 2 hours, or until beef is fork-tender.
Remove steak, shred with two forks, and return to the sauce. Simmer uncovered for 10 more minutes to thicken.
Taste. Add more salt and pepper, to taste, if needed.
Serve hot with white rice, seasoned black beans and sweet fried plantains for a true Cuban plate.