Season the beef pieces generously with salt and pepper.
In a large heavy pot or Dutch oven, cook the diced bacon (or pancetta) over medium heat until crisp. Remove and set aside leaving the rendered fat.
Sear the beef pieces in the bacon fat over medium-high heat until browned on all sides. Remove and set aside.
Add the onion, carrot, and celery to the pot and sauté until vegetables are softened, about 5-7 minutes.
Add the garlic and red pepper flakes (if using), cook for 1 minute until fragrant.
Return the beef and bacon to the pot.
Pour in the beef broth and crushed tomatoes.
Add thyme, rosemary, Italian seasoning, bay leaves, and more salt and pepper to taste.
Bring the mixture to a gentle simmer, then cover and reduce heat to low.
Cook for 3 hours, turning the beef occasionally, until the meat is tender and easily shredded.
Remove the bay leaves before serving.
Serve hot with the rich sauce spooned over the top.