Here is Ana Sortun's recipe (from Oleana in Cambridge, MA) for braised short ribs.
It was published in "The way we cook" by Sheryl Julian and Julie Riven.
Cook these shortribs at least 1 day before serving.
2 Tbsp olive oil
1 Tbsp butter
4 large Spanish onions, halved and thinly sliced (I use 8 yellow onions)
1/2 tsp coarse salt, or to taste
1/2 tsp black pepper, or to taste
2 cups balsamic vinegar
1 cup low-sodium soy sauce (I use regular soy sauce)
1/2 cup dry white wine
1/2 cup water
1/2 cup dark brown sugar
8 shortribs (or 4 Lb of some other tough cut of beef that's good for braising, like chuck roast)
4 garlic cloves, finely chopped
2 whole start anise (optional)
1 bay leaf
Preheat the oven to 350F.
Cook onions with salt and pepper in a large oven-safe casserole in oil and butter on med-high heat, stirring occasionally until softened, about 5 minutes. Turn down the heat to med-low and cook another 10 minutes, or until golden brown. Remove onions from the casserole and set aside.
Pour vinegar, soy sauce, wine, water, sugar, garlic, anise, and bay leaf into the casserole and bring to a boil. Add short ribs and cover them with onions and return the liquid to boil. Cover casserole and transfer it to the oven. Cook for 3 hours or until fork tender. (If you have time, it's even better to cook it longer at a lower temperature. I usually do it for 6 hours at 275F).
Refrigerate meat and liquid separately overnight. The fat on top of the liquid will solidify. Carefully lift it off and discard. Combine as many shortribs as you are serving that day with some of the balsamic soy liquid and simmer on the stove top until reheated.
By the way, these shortribs freeze beautifully. Just freeze the meat and liquid separately.