Return the short ribs to the pot and stir in the thyme sprigs, bay leaf, garlic and tomato paste. Add the wine and bring to a simmer, then cook until reduced by half, about 5 minutes. Add the stock and return to a simmer. Cover and cook on very very low, until the short ribs are falling off the bone. 2 hours 30 minutes.
Shred the meat, discarding the sinew and the bones, and toss the meat with 1 cup of the broth. Set aside.
Transfer to the oven and bake until golden and bubbly, about 10 minutes.