Generously sprinkle salt and pepper over all sides of the English cut short ribs, allowing them to sit for about 10 minutes at room temperature.

Heat 1 tablespoon of oil and 1 tablespoon of butter in a large skillet over high heat for about 2 minutes. Sear the short ribs for about 30 seconds on each side.

Transfer the browned short ribs to the slow cooker, arranging them in a single layer.

Lower the heat, and in the same skillet, sauté 1 diced onion and 3 chopped garlic cloves for 3-4 minutes until translucent. Add beef broth, red wine, brown sugar, tomato paste, Worcestershire sauce, and thyme, stirring for 10-15 minutes.

Pour the sauce mixture over the short ribs in the slow cooker.

Cover the slow cooker and cook on low for 8 hours or high for about 4 hours until fork-tender.

After cooking, remove ribs and whisk together 1 tablespoon of cornstarch with 1 cup of the sauce until smooth. Stir back into the slow cooker and let thicken for about 5 minutes.