Heat a large pot or dutch oven over medium-high heat. Add the pancetta and cook, stirring occasionally, until fat is rendered and the pancetta is just crisp, 4 to 5 minutes.
Add the anchovy, onion, carrot, celery and garlic and cook, mashing up the anchovies so that they break into a paste-like consistency. Continue to cook, stirring, until the veggies are tender, 5 to 7 minutes.
Add the ground beef, pork, veal, salt and pepper. Cook, breaking up the meat with the back of a spoon, until the meat is just cooked through (no longer pink), about 7 minutes. Drain off excess fat if necessary... (I like to leave a little in there though for flavor!)
Add the wine and cook, stirring, until the wine is reduced by half, about 3 minutes. Add the san marzano tomatoes, the tomato sauce, and the tomato paste and stir until well combined. Bring to a boil.
Once the sauce is boiling, reduce to a light simmer (low heat). Add the parmesan cheese rind, the bay leaves, and the thyme. Cook, covered and stirring occasionally, until the flavors have melded and the meat is extremely tender and flavorful-- at least 4 hours, but I like to cook mine all day!
About 30 minutes prior to serving, stir in the cup of milk and continue to cook, uncovered and slightly simmering, until ready to serve. Taste and add more salt and pepper to taste, if desired.
Remove and discard the cheese rind, bay leaves, and thyme bundle.
Serve the sauce tossed in pasta cooked al dente. Garnish with freshly grated parmesan and fresh thyme leaves. Enjoy!