Heat the olive oil in a large, heavy-bottomed pot over medium-high heat. Add the beef chunks in batches, making sure not to overcrowd the pot. Sear on all sides until deeply browned, then remove and set aside.
Reduce the heat to medium. Add the chopped onion, carrots, and celery to the same pot. Cook slowly, stirring often, until the vegetables soften and become lightly golden, about 8–10 minutes.
Add the minced garlic and cook for about 30 seconds, just until fragrant. Stir in the tomato paste and cook for another 2 minutes, allowing it to darken slightly and deepen in flavor.
Return the seared beef to the pot. Pour in the crushed tomatoes and beef stock, scraping the bottom of the pot to release all the flavorful browned bits.
Add the bay leaves, oregano, thyme, smoked paprika, black pepper, salt, and sugar if using. Stir well and bring the sauce to a gentle simmer.
Lower the heat to the lowest setting, partially cover the pot, and let it simmer slowly for 2 1/2 to 3 hours. Stir occasionally. The beef should become extremely tender and easy to shred.
Once the beef is fully cooked, use two forks to shred it directly in the pot. Continue simmering uncovered for another 20–30 minutes, until the sauce thickens and coats the beef beautifully.
Taste and adjust seasoning if needed. Remove the bay leaves before serving.
Cook the pasta in well-salted water according to package instructions until al dente. Reserve some of the pasta water before draining.
Toss the cooked pasta with the beef ragu, adding a splash of reserved pasta water if needed to loosen the sauce and help it cling to the noodles.