Preheat oven to 350°. Season short ribs with salt, pepper and smoked paprika. Heat canola oil in a large Dutch oven over medium-high. Brown short ribs on all sides, about 1-2 minutes each side. Place ribs on a plate with drippings and set aside but reserve about 3 tbsp of drippings from the pot to saute onions and garlic.
Add onions and sauté for a 2 minutes, then add garlic until fragrant, approximately 1 minute. Stir in beef stock and worcestershire sauce.
Whisk flour and water together in a small bowl until lumps disappear and combine with stock mixture. Add tomato paste, stirring continuously as sauce begin to thicken, add short ribs with any leftover juices into the pot.
Add rosemary to pot, laying each spring over two short ribs, cover an oven safe dish and transfer to oven and bake for 2 to 2 1/2 hours. Serve over mashed potatoes or vegetables.