Season all sides of the beef short ribs with salt and pepper. In a large skillet over medium heat, sear each piece of short rib until nicely browned on all sides—about 20 seconds per side.

Transfer the short ribs to a large crockpot. Add in the baby carrots, sliced mushrooms, beef broth, apple vinegar (if using), tomato paste, unsalted butter, bay leaf, fresh thyme sprigs, and minced garlic. Stir gently to combine all ingredients.

Cover the crockpot and set it to cook on low for approximately 8 hours until the meat is tender.

Once cooking time is up, carefully remove the short ribs and vegetables from the crockpot. Discard any herbs used during cooking and serve immediately.