1. Heat 1 tablespoon of the olive oil in a large, heavy saucepan until
shimmering. Add the onion, carrot, celery and pancetta and cook
over moderate heat, stirring occasionally, until the vegetables
are softened but not browned, about 8 minutes. Scrape the
vegetable mixture into a large bowl.
2. Add the remaining 3 tablespoons of olive oil to the saucepan
and heat until just shimmering. Add the beef, veal and pork and
cook over moderately high heat until just barely pink, about 5
minutes. Return the vegetable mixture to the saucepan. Add the
garlic and cook over high heat until fragrant, about 1 minute. Add
the wine and cook, stirring occasionally, until almost evaporated,
about 8 minutes. Stir in the tomatoes and their juices, the chicken
stock, thyme and bay leaf. Season with a generous pinch of salt
and pepper and bring to a boil over high heat. Cover partially
and cook over moderately low heat for 1 hour. Discard the bay
leaf. Stir in the heavy cream and cook the sauce just until heated
3. In a large pot of boiling salted water, cook the pasta until al
dente. Drain well, return to the pot and toss with the sauce. Serve
the pasta in deep bowls and pass the Parmesan at the table.
MAKE AHEAD The sauce can be refrigerated for up to 3 days and
frozen up to 1 month.