Step 1Combine the pork, veal, fennel seeds, egg, bread crumbs, salt and minced onion in a large mixing bowl. Stir or work with your hands until the mixture is homogenous. It will be very wet.
Step 2Heat the olive oil over medium-high heat in a large skillet until it is hot enough to sizzle when a bit of meat is added to it. Pinch off portions of the meat mixture and roll them into balls about the size of walnuts (much bigger and they begin to fall apart as they cook). As you make each one, add it to the olive oil.
Step 3Cook the meatballs until they are browned on one side, 2 to 3 minutes. Do not move them around too much or they won't brown well. As each meatball browns, flip it to brown another part. The fennel seeds will pop out of the skillet; use a splatter guard or be very careful. When all the meatballs are well-browned, remove them with a slotted spoon and reserve them on a platter.
Step 4Pour off all but 1 teaspoon of the fat in the skillet, being careful to reserve all of the bits of browned meat. Add the onion and stir, scraping the bottom. As the onion cooks, it will release moisture, which will loosen the browned bits sticking to the pan. When the onion is soft, after about 5 minutes, add the garlic and cook until it is fragrant, about 1 minute. Add the white wine and cook just until it loses its raw smell, about 1 minute. Add the tomato pulp and stir to mix well.
Step 5Gently slide the meatballs back into the tomato sauce, cover and cook over medium-low heat until the meatballs are firm and the sauce has thickened slightly and reduced, gently stirring occasionally to coat the meatballs with the sauce. This will take about 45 minutes.
Step 6Taste the sauce about 5 minutes before serving. Add more salt if needed, then sprinkle the chopped fennel fronds over the top, if you're using them, replace the lid and finish the cooking.