Sear the Ribs (Optional but Recommended):
Pat short ribs dry and season with salt, pepper, and a light dusting of flour. Heat oil in a skillet over medium-high heat. Brown the ribs on all sides in batches, about 2–3 minutes per side. Transfer to slow cooker.
Sauté Aromatics:
In the same skillet, add onion and cook for 3–4 minutes. Stir in garlic and tomato paste; cook another minute. Add Worcestershire sauce and a splash of broth to deglaze, scraping up brown bits.
Add to Slow Cooker:
Transfer onion mixture to the slow cooker. Add remaining broth, wine, thyme, and bay leaves. Stir gently, nestling ribs into the liquid.
Cook:
Cover and cook on LOW for 8 hours or HIGH for 4–5 hours, until ribs are tender and falling off the bone.
Make the Gravy (Optional):
Remove ribs and cover loosely with foil. Skim excess fat from the cooking liquid. For a thicker gravy, stir in a cornstarch slurry and cook on high for 10–15 minutes, until thickened.
Serve:
Spoon rich gravy over ribs and garnish with fresh parsley. Serve with mashed potatoes, polenta, or crusty bread.