Heat olive oil in a large, heavy-bottomed pot or Dutch oven over medium heat, then add pancetta or bacon and cook until crispy, about 5-7 minutes. Remove the crispy pancetta/bacon and set aside, leaving the rendered fat in the pot.

Add the chopped onion, carrots, and celery to the pot and sauté for about 8-10 minutes until softened. Stir in the minced garlic and cook for an additional minute until fragrant.

Increase heat to medium-high and add the ground beef, breaking it up with a spoon. Cook until the beef is browned and any liquid has evaporated, draining any excess fat if necessary.

Stir in the tomato paste and cook for 2 minutes, then pour in the red wine and bring to a simmer, scraping up any browned bits from the bottom of the pot. Cook until the wine has mostly evaporated.

Add the crushed tomatoes, beef broth, dried oregano, salt, and pepper to the pot. Stir well to combine, bring the sauce to a gentle simmer, then reduce heat to low.

Cover the pot and let the Bolognese simmer for at least 1.5 to 2 hours, or up to 3 hours for deeper flavor, stirring occasionally. The sauce should be thick and rich.

Remove the lid during the last 30 minutes of cooking to allow the sauce to thicken further, then stir in the chopped fresh basil and adjust seasoning.

While the sauce simmers, cook the spaghetti according to package directions until al dente.

Serve the Bolognese sauce over hot spaghetti, garnished with grated Parmesan cheese and fresh basil leaves, along with the reserved crispy pancetta/bacon.