01 - Pat the beef cubes thoroughly dry with paper towels and season generously with salt and freshly ground black pepper on all sides.
02 - Heat the olive oil in a large, heavy-bottomed pot or Dutch oven over medium-high heat until shimmering. Working in batches to avoid crowding, sear the beef cubes until deeply browned on all sides, approximately 3-4 minutes per batch. Transfer the browned beef to a plate and set aside.
03 - In the same pot with the rendered drippings, add the chopped onion, sliced carrots, and chopped celery with a pinch of salt. Sauté over medium heat for 5 to 6 minutes until the vegetables have softened and the onions become translucent. Add the minced garlic and cook for an additional minute until fragrant.
04 - Stir in the tomato paste and cook for 2 minutes, allowing it to caramelize slightly. Pour in the dry red wine, scraping the bottom of the pot with a wooden spoon to deglaze and lift any browned bits. Allow the wine to reduce by half, approximately 2 to 3 minutes.
05 - Return the seared beef and any accumulated juices back to the pot. Add the diced tomatoes, beef broth, bay leaves, thyme sprigs, and rosemary. Stir everything together thoroughly and bring the mixture to a gentle simmer.
06 - Cover the pot with a tight-fitting lid, reduce the heat to low, and cook for 1 hour and 30 minutes, stirring occasionally to prevent sticking and ensure even cooking.
07 - Add the cubed potatoes to the pot, adjust the seasoning with additional salt and pepper if needed, and continue cooking uncovered for an additional 30 minutes, or until both the potatoes and beef are fork-tender and the sauce has thickened to a rich consistency.
08 - Remove and discard the bay leaves and herb stems. Ladle the hot spezzatino into bowls and serve alongside crusty bread, creamy polenta, or mashed potatoes.