Melt butter with olive oil in a large saucepan over medium heat; gently cook onion, celery, and carrot together; add 1 or 2 whole bay leaves and a pinch of salt. Cook just until the onion turns translucent– no longer than 5 minutes. Stir ground beef, ground pork and ground veal into vegetables and cook, stirring constantly. Cook until meat is crumbly and gently browned, about 5 minutes. Drain excess fat, then season mixture with 1 1/2 teaspoon salt, black pepper, cayenne pepper, and nutmeg.
Pour milk into mixture and gently bring just to a simmer. Continue to simmer about 5 minutes, until most of the milk has evaporated and is integrated into the sauce.
Raise heat to medium high, then pour good-quality white wine into the sauce mixture. Cook and continue to stir for 5 minutes or so, until the white wine has evaporated
Pour San Marzano tomatoes with juice into a large mixing bowl. Crush gently with a spoon, leaving somewhat chunky. Add tomatoes paste to the sauce along with 2 cups beef stock.
Now the hard part– waiting! Reduce the heat to low and simmer, simmer, simmer. You’ll need to stir often. Not only are you waiting for the sauce to thicken, but you’re also waiting for the heat and stirring to gently integrate all the ingredients. Plan on at least 3 hours. Longer is better– some swear by slowly simmering for 6 hours! Don’t hurry your Bolognese– it will be worth it! Add more stock if sauce thickens too quickly.
When the sauce is nearly ready, heat 4 quarts of salted water to the boil. Add the pappardelle and cook according to instructions to just al dente. Save back half a cup of the pasta water while you drain the pasta.
In a separate sauce pan, place 2 large spoonful of sauce. Heat to medium-high. Add drained pasta and stir to lightly coat each ribbon of pasta. Add rest of sauce, stir and then begin adding pasta water a Tablespoon at a time , stirring until pasta is fully coated.
Serve immediately with grated Parmesan cheese on the side. Get ready to be asked to make again next week!