For the meatballs
1. Preheat oven to 375°.
Sauté fennel and onion in the olive oil over medium-high heat until softened and the onion is translucent. Add a few pinches of salt and the garlic. Sauté until you smell the garlic, then remove from the heat. Transfer contents of pan to a plate and chill in your refrigerator.
2. Place the first 10 ingredients for the meatballs in a large mixing bowl.
Thoroughly mix the meatball ingredients in the mixing bowl. When the sautéed onion mixture is cool, add this to the mixing bowl. Use clean hands to really incorporate all of the ingredients, do not over-mix. Sauté a small chunk of the mixture to check for seasoning and adjust to taste with salt and pepper.
3. Roll the meatball mixture into golf ball-sized rounds (about 2 tablespoons each) and place on a cookie sheet while you work. When finished, refrigerate while you work on the marinara sauce.
4. To cook the meatballs, sauté them in the remaining olive oil in batches and finish by baking them in a rimmed sheet-pan. (If you have a muffin pan, then use my preferred method: Place each ball in lightly greased wells of the muffin pan, turn the meatballs over half way through cooking to evenly brown the surface. You’ll notice that the balls will self-baste while cooking in the muffin wells). Cook the meatballs for about 30 minutes at 375° or until the internal temperature is about 140° to 150° degrees. Be careful to watch for rendered fat when you pull them out of the oven.
5. Just before serving, transfer the meatballs to the pan of marinara sauce and simmer for a few more minutes.
To serve, arrange the meatballs on a serving platter with some of the marinara. Garnish with a drizzle of olive oil, grated Parmigiano-Reggiano, and small handful of whole Italian flat-leaf parsley leaves.