Preheat an oven. Flanken can either be left whole or each rib can be cut in half for smaller portions. Season flanken ribs on all sides generously with Kosher salt and black pepper.
Heat a large dutch oven over high heat until very hot. Add canola oil then sear ribs until browned on both sides. Transfer seared flanken to a plate and set aside while you repeat with remaining ribs. Set aside.
To the hot pan, add diced onion and sliced carrots, then cook. Add minced garlic and cook, then stir in tomato paste. Pour in red wine, then use a spatula to scrape any brown bits off the bottom of the pan. Allow wine to cook down, then add beef stock and ground cinnamon. Stir to combine.
Return seared flanken ribs to the pan, then add prunes and rosemary. Just enough so the ribs are mostly submerged. They will cook down and shrink a bit as they cook!
Place a lid on top, then cook until rib meat is tender and pulls gently away from the bones. Discard rosemary stems. Allow to cool slightly before serving.