Best Bolognese Sauce

In a large dutch oven over medium-high heat, heat oil. Add onion, carrot, and celery, and cook until soft, about 7 minutes. Stir in beef and garlic, breaking up meat with back of a spoon. Cook until no longer pink and lightly seared, about 8 minutes.  Add wine, and bring mixture to a simmer. Cook until wine is mostly reduced. Stir in tomatoes, tomato paste, stock, and bay leaf, then reduce heat and simmer for 1 hour, allowing flavors to meld.  Discard bay leaf, then gradually stir in milk. Cover with a lid slightly ajar and simmer, stirring occasionally, until milk is fully incorporated, about 45 minutes. Season with salt and pepper.