Heat olive oil in a large pot or Dutch oven over medium heat, then add the diced pancetta or bacon and cook until crispy. Remove the pancetta with a slotted spoon, leaving the rendered fat in the pot, and set aside.

Add the ground beef to the pot and cook, breaking it up with a spoon, until it is browned all over; drain any excess fat if necessary.

Add the chopped onion, carrots, and celery to the pot and cook until softened, about 8-10 minutes.

Stir in the minced garlic and cook for another minute until fragrant, being careful not to burn it.

Pour in the red wine and bring to a simmer, scraping up any browned bits from the bottom of the pot, and cook until the wine has mostly evaporated, about 5-7 minutes.

Add the crushed tomatoes, beef broth, bay leaves, and oregano to the pot; season with salt and black pepper to taste. Bring the sauce to a gentle simmer, then reduce the heat to low, cover, and let it cook for at least 2-3 hours, stirring occasionally, or even longer for a richer flavor.

About 20 minutes before the sauce is done, cook the spaghetti according to package instructions until al dente, usually 8-10 minutes.

Drain the spaghetti and either toss it directly with the Bolognese sauce or serve the sauce over the spaghetti. Garnish each serving with grated Parmesan cheese, fresh basil, and the reserved crispy pancetta if desired.