• 
  For the sauce:
• 1 (14-ounce) or 1/2 (28-ounce) can whole peeled tomatoes in juice, preferably San Marzano
• 1 1/2 to 2 1/2 cups water
• 1 tablespoon tomato paste, preferably double concentrated
• 1 teaspoon beef base (available in some supermarkets and specialty food stores) or 1 beef bouillon cube
• 1 celery rib, roughly chopped
• 1/2 medium onion, roughly chopped
• 1/2 medium carrot, roughly chopped
• 3 tablespoons unsalted butter
• 2 ounces sweet Italian sausage, removed from casing
• 2 ounces pancetta or slab bacon, finely chopped
• 3/4 pound ground beef (not lean)
• 3/4 pound ground pork
• 1/2 pound ground veal
• Fine sea salt
• Freshly ground black pepper
• 1 cup dry red wine
• 1 bay leaf
• 3/4 cup whole milk
• Freshly grated nutmeg
•  
• For serving:
  
• Fresh tagliatelle, or other pasta, cooked until tender in salted water
• Freshly grated Parmigiano-Reggiano cheese

Purée tomatoes and their juice in blender until smooth; set aside.

In a small saucepan, bring 1 1/2 cups water to a simmer; whisk in tomato paste and beef base. Remove from heat; set aside.

Make a battuto (the foundation for many Italian soups, stews and sauces) by finely chopping together (by hand) celery, onion and carrot.

Heat butter over medium-low heat until melted and foaming; add battuto, sausage and pancetta. Cook, stirring with a wooden spoon, until sausage is broken into small bits, then continue cooking, stirring frequently, until vegetables are softened (do not brown), about 25 minutes.

Add beef, pork and veal; increase heat to medium. Cook, stirring until meat is broken into small bits, then season lightly with salt and pepper. Cook, stirring constantly for 10 minutes more (do not brown).

Add wine; bring to a boil and cook until wine and juices in pot are mostly evaporated, 3 to 5 minutes. Add reserved puréed tomato, reserved beef base mixture and bay leaf.

Cook ragù at the barest simmer, stirring occasionally (making sure to stir into edges of pot), until meat is very tender and sauce is thick (as sauce thickens, add water, bit by bit, if necessary, to keep sauce moist and just barely liquid), about
2 1/2  hours.

Add milk and continue cooking for 30 minutes more. Stir in pinch nutmeg. Season to taste with salt and pepper. 

To serve:
Toss the ragù with pasta using 1 1/2 to 1 3/4 cups of sauce per pound of pasta. Serve immediately with cheese.