Step 1

Season ribs with salt and pepper. Rub miso all over ribs to evenly coat. Tightly wrap in butcher paper or plastic, transfer to a large resealable bag or container, and refrigerate at least 24 hours and up to 3 days. Bring to room temperature 1 hour before cooking.

Step 2

Preheat oven to 325°F. Unwrap ribs and wipe off excess miso with a paper towel. Heat a wide pot over medium; swirl in 2 tablespoons oil. Working in two batches, brown ribs on meaty sides, about 5 minutes (if pot bottom darkens too quickly, wipe clean between batches). Transfer to a plate.

Step 3

Swirl remaining 1 tablespoon oil into pot. Add shallots, fennel, celery, ginger, and thyme; season with salt and pepper. Cook, stirring occasionally, until vegetables turn golden in places, 8 to 10 minutes. Stir in tomato paste, allspice, and bay leaf and cook 1 minute. Add wine and boil, scraping up browned bits from bottom of pot, until mostly evaporated, 1 to 2 minutes.

Step 4

Return ribs and accumulated juices to pot, bone-sides down. Crush tomatoes into pieces with your hands or a masher; add to pot with tomato juices, 1 1/2 cups broth, and orange zest and juice. If necessary, add more broth to just cover ribs. Bring to a simmer.

Step 5

Cover pot and transfer to oven; braise 2 hours. Remove lid and continue to braise, spooning liquid over ribs a few times, until meat is fork-tender, 1 to 1 1/2 hours more. Transfer ribs to a platter and loosely cover to keep warm.

Step 6

Strain braising liquid through a mesh sieve, pressing on solids to extract as much liquid as possible; discard solids. Spoon excess fat from liquid (or use a fat separator). Transfer liquid to a small saucepan and bring to a boil.

Step 7

Meanwhile, whisk together remaining 1/2 cup broth and flour until smooth. Slowly whisk into braising liquid. Boil, whisking constantly, until thickened slightly, about 30 seconds. Sprinkle ribs with fennel fronds and pomegranate arils and serve with gravy.