Season the short ribs generously with salt and pepper. Heat olive oil in a large skillet over medium-high heat. Sear the ribs on all sides until nicely browned. Transfer the ribs to the crockpot.

In the same skillet, add the sliced onion and minced garlic. Cook for about 2-3 minutes until softened. Stir in the tomato paste and cook for another minute, then transfer the onion and garlic mixture to the crockpot.

Pour a small splash of beef broth into the skillet to scrape up any browned bits from the bottom. Transfer this to the crockpot with the ribs.

Add the remaining beef broth, Worcestershire sauce, dried thyme, fresh rosemary, and bay leaf to the crockpot.

Cover the crockpot and cook on low for 8 hours, or until the ribs are fork-tender.

Remove the bay leaf and rosemary sprig before serving. Serve the ribs with their juices over mashed potatoes, rice, or creamy polenta.