In a large oven-safe saucepan or Dutch oven, cook the diced beef bacon over medium heat until browned, then remove it and set aside.

Season the beef pieces with salt and pepper. Sear them in the rendered bacon fat over medium-high heat until a deep brown crust forms on each side, about 4–6 minutes per side. Remove the beef and set aside.

Add the onion, carrot, and celery to the pan and cook over medium heat, stirring occasionally, until the vegetables are softened, about 7–10 minutes.

Stir in the chopped garlic and, if using, the red pepper flakes. Cook until fragrant, about 1 minute.

Pour in the beef broth and add the crushed tomatoes, thyme, rosemary, Italian seasoning, bay leaves, and the cooked beef bacon; mix well, then return the seared beef to the pot.

Choose your cooking method: (1) For stovetop, bring to a boil, reduce to low, cover, and simmer until the beef becomes fall-apart tender, about 2–4 hours; (2) For oven, cover and bake in a preheated 275°F (140°C) oven for 2–4 hours; (3) For slow cooker, transfer everything to the insert and cook on LOW for 8–10 hours or HIGH for 4–6 hours.

Once the beef is extremely tender, remove the bay leaves, taste the sauce, and adjust with additional salt and pepper as needed. Serve and enjoy.