Heat the olive oil in a large, heavy-bottomed pot over medium heat. Add the onions, celery, carrots and garlic, and sauté for a few minutes until the vegetables soften.
Add the beef and season with salt and pepper. Break up the ground beef and cook until it's browned and crumbled. stirring occasionally.
Add the milk and allow it to simmer until it has mostly evaporated, stirring occasionally, in order to help tenderize the beef, about 10 minutes.
Add crushed tomatoes, tomato paste, bay leaf, oregano and nutmeg. Mix to combine, bring mixture to a boil and then simmer on low uncovered for at least 30 minutes, but preferably 1-2 hours. Simmering for longer will enhance the flavor. Remove from heat and remove the bay leaf.
When ready to serve, bring a large pot of salted water to a boil. Serve the cooked pasta in individual bowls and spoon the Bolognese sauce over it. Garnish with freshly chopped parsley and grated Parmesan cheese, if desired.
