Heat the olive oil and butter in a large saute pan over medium heat
When the butter has melted and looks foamy add the onion, celery and carrots and cook for 2 minutes. Add the garlic and cook another minute.
Add the pancetta and beef and cook, stirring about 4-5 minutes or until the beef is no longer pink. Season with salt and pepper.
Add the wine and cook the mixture until the liquid has almost completely evaporated. Add the tomatoes, beef stock and oregano. Break up tomatoes with a large wooden spoon. Bring the sauce to a simmer and cook for about 2 hours, stirring occasionally.
Add the milk and cook, stirring occasionally, until the liquid has evaporated, about 10 minutes