Preheat oven to 300°. In a large Dutch oven, heat 2 tablespoons canola oil over medium-high heat. Add onion, carrot, and celery; cook, stirring occasionally, until lightly browned, approximately 4 minutes. Add garlic; cook 1 minute. Remove vegetable mixture from pan.
Add remaining 2 tablespoons canola oil to pan. Sprinkle ribs with 2 teaspoons salt and 1 teaspoon pepper. Add half of ribs to pan; cook until browned on all sides, approximately 8 minutes. Remove from pan. Repeat procedure with remaining ribs.
Return vegetable mixture and ribs to pan. In a small bowl, whisk together tomato paste and cocoa powder. Add tomato paste mixture, broth, wine, thyme, and bay leaves to pan.
Bake, covered, until tender, approximately 2 hours and 45 minutes, basting occasionally with cooking liquid. Discard thyme and bay leaves. Stir in remaining 1 teaspoon salt, remaining 1⁄4 teaspoon pepper, and vinegar. Garnish with thyme sprigs, if desired. Serve with braising liquid.
Recipe by Southern Cast Iron at https://southerncastiron.com/red-wine-braised-short-ribs/