Preheat oven to 350 degrees.
Heat olive oil in a Dutch oven over medium-high heat. Generously season the short ribs with salt and black pepper. Working in batches, place the short ribs in the hot oil and sear well on all sides, approximately 4-5 minutes per side. Transfer to a plate.
Add the onion, carrot and celery to the hot oil. Reduce heat to medium-low, add a pinch or two of salt and cook, stirring often until very soft, approximately 10-12 minutes.
Add the garlic, stir until fragrant (15 seconds), then add wine. Bring to a boil and cook 2-3 minutes to reduce slightly.
Add beef broth, crushed tomatoes, Italian seasoning and bay leaves.
Place short ribs back into the pot, cover securely with aluminum foil or parchment paper then place the lid on the pot and place in the oven. Cook for 2-2 1/2 hours.
Add the rosemary and place back in the oven for 30 minutes or until ribs are extremely tender.
Take short ribs out of the Dutch oven and place in a bowl. Remove and discard bay leaves. Cover to keep warm.
Place flour in a small bowl. Remove approximately 2/3 cup of the braising liquid. Add it to the flour in the bowl and whisk to form a thick slurry. Whisk the slurry into the braising liquid and stir. Bring to a simmer over medium-high heat. Cook 4-5 minutes or until thickened and flour is cooked. Place short ribs back into the Dutch oven. Let sit off the heat for 10 minutes or so. The sauce will thicken more upon standing. (Should be more of a sauce rather than a gravy.)
Serve over Cauliflower Leek Puree.