Begin by heating a large skillet over medium-high heat and adding a splash of olive oil. Generously season your beef short ribs with salt and pepper, then sear the meat in the hot skillet for about 3 minutes on each side until they develop a deep, golden-brown crust.

In the same skillet, remove excess fat and toss in the diced onions and minced garlic. Sauté these aromatics for about 5 minutes until the onions are soft and translucent.

Pour in one cup of red wine, scraping the brown bits from the bottom of the skillet with a wooden spatula. Bring the mixture to a gentle simmer for about 2 minutes.

Carefully move the browned ribs, cooked onions, and garlic-wine mixture into your slow cooker. Add the beef broth, balsamic vinegar, brown sugar, and dried thyme, stirring gently to combine.

Cover the slow cooker and cook on low for 6 to 8 hours or high for 4 to 5 hours. Ribs are done when they're tender and can be easily pulled apart with a fork.

Once cooked, remove the tender short ribs and plate them, drenching them in the cooking liquid. Serve with creamy mashed potatoes or crusty bread.