
In a large Dutch oven, heat a generous drizzle of olive oil and sear the short ribs on all sides. Remove from the pot.
Add a touch more olive oil and the red onion chunks. Cook for 2-3 minutes, or until slightly softened. Add in garlic and tomato paste, and cook until the garlic is fragrant, about 1-2 more minutes.
Add in the balsamic vinegar, red wine, and coconut sugar and cook down for 2-3 minutes, until slightly thickened
Cook covered for 2 to 2 ½ hours, or until fork tender and the sauce reduced and slightly thickened, turning the short ribs in the sauce about half way through (if desired).
Remove from oven. Remove thyme and bay leaves. Stir in butter until fully melted and incorporated into the sauce.
For the polenta. Stir polenta, broth, and milk together in a saucepan over medium heat; cook and whisk until the polenta is heated through completely and creamy, about 5 minutes. Add more liquid if needed (should be the consistency of grits or oatmeal).