In a Dutch oven over a MEDIUM-HIGH flame, add 2 tbsp. butter, diced celery, onion and carrot (save the garlic). Sauté for 10 minutes, stirring occasionally.
While vegetables sauté, paper towel-dry 6 short ribs. Liberally sprinkle each side with kosher salt and freshly ground pepper. Once vegetables are done sautéing, remove them into a bowl and set aside. Add 2 tbsp. butter to the pot and turn heat to HIGH. Sear short ribs on all sides, and remove.
Preheat oven to 325 F. (165 C.). Remove fat from pot (it’s ok if a few tablespoons are left, but you don’t want more than 2 tablespoons). Add 2 more tbsp. butter. Add 4 smashed garlic cloves and sauté on HIGH for 1 or 2 minutes. Pour in full bottle of cabernet. Reduce wine for 10 minutes. You should have only about 1 cup of red wine once it’s reduced.
Add back sautéed vegetables and place short ribs bone-up in the pot. Pour in beef broth, just enough to cover the ribs. Add a few sprigs of thyme and rosemary. Cover the pot, place in the oven, and leave for 2½ hours.
After 2 or so hours, place 12 oz. blackberries and 1 tsp. brown sugar in a saucepan. Break up berries with a potato masher as best you can. Allow it to simmer and reduce for 10-15 minutes. Pour over a mesh strainer, and push through reduction with a spoon to separate the seeds. Discard seeds.
Remove pot from oven, and remove short ribs into a bowl. In a separate bowl from the blackberry reduction, pour the pot over a strainer to separate sauce. Discard vegetables and herbs. Use a fat separator to remove all of the fat that has risen to the top, then combine with blackberry reduction. Place sauce back into the dutch oven on the stove. Over a HIGH flame, reduce further for 10 minutes.
If you would like the sauce to be thicker, simply add 1-2 tbsp. flour to a small bowl. Add 3-4 tbsp. of the sauce to the bowl and stir. Make sure there are no lumps in the slurry. Reduce heat, and pour the slurry into the pot. Carefully stir to thicken the sauce. Give it a taste and see if it could use a little more salt or pepper. Place ribs back in the pot to cover with sauce, and serve.