Put the garlic, celery, carrot, onion and oregano leaves in a food processor and pulse to chop into small pieces.
Heat the olive oil in a medium Dutch oven or heavy pot over medium heat. Add the chopped vegetables and cook, stirring once or twice, until they start to soften, about 5 minutes. Stir in the pork, beef, tomato paste, and some salt, pepper and red pepper flakes and cook, stirring often, until the meat is browned, about10 minutes.
Add the diced tomatoes, crushed tomatoes and basil sprigs. Bring the sauce to a simmer, reduce the heat to low and cook, stirring occasionally, until thickened, 1 to 1 1/2 hours.
Just before the sauce is done, bring a large pot of salted water to a boil over high heat and cook the penne until al dente, according to package directions. Drain and return to the pasta pot. Spoon about 1 cup of sauce into the penne and stir to coat. Serve the penne topped with more sauce, some torn basil and a sprinkle of Parmesan.