Balsamic Braised Short Ribs

Name: Balsamic Braised Short Ribs
Ingredients: 2 lb. (1 kg) boneless beef short ribs or 3 1/2 lb. (1.75 kg) bone-in short ribs; Kosher salt; 2 Tbs. all-purpose flour; 1 Tbs. vegetable oil, plus more as needed; 8 medium shallots, peeled and thinly sliced; 6 garlic cloves, thinly sliced; 1/4 cup (2 oz./60 g) tomato paste; 2 cups (16 fl. oz./500 ml) dry red wine, such as Chianti; 4 cups (32 fl. oz./1 l) beef stock; 1/2 cup (4 fl. oz./125 ml) balsamic vinegar; 2 Tbs. light brown sugar; Leaves from 10 fresh thyme sprigs; 1 Tbs. crushed red pepper flakes; Finely chopped fresh chives for serving