MEATBALLS: Pour the milk over the breadcrumbs in a small bowl. Stir them together and set them aside for at least 10 minutes for the crumbs to soften.
Mix the pork, beef, and veal together thoroughly in a large mixing bowl. Stir in the salt and a generous amount of black pepper, then add the smoked paprika and cayenne.
Stir in the chopped parsley, sage, onion, garlic and Parmesan. Mix with your hands until these are very thoroughly distributed through the meat.
Stir in the breadcrumbs and milk, as well as the eggs, and mix thoroughly.
Shape and cook the meatballs immediately, or refrigerate the meat for up to 24 hours. You can also freeze the meat (in one big lump or as shaped meatballs) in a sealed container for up to 3 months.
SAUCE: Dice the onion and mince the garlic. Heat a large, deep saute pan over medium high heat. (It should be large enough to hold the sauce ingredients, as well as most of the meat.)
Saute the onion and garlic in the olive oil until very soft — about 10 minutes, turning the heat down if necessary.
Stir in the tomato paste and fry for a minute or two, stirring until well-incorporated. Pour in the wine and broth and bring to a simmer, then add the tomatoes, salt, and a generous amount of black pepper.
Place the rosemary sprig on top, bring to a simmer and cook for 30 to 60 minutes, covered. When the sauce has developed a deep, rich flavor, turn off the heat and puree with an immersion blender (or in a standing blender) until smooth.
Serve the sauce over the meatballs with pasta or greens.