Begin by soaking stale bread in milk until it’s softened. Blend this softened bread with parsley into a light, fluffy paste.
Combine the paste with ground beef, cheeses, chili flakes, fennel seeds, and breadcrumbs in a mixing bowl. Use your hands to mix everything until evenly combined, but don’t overwork the mixture. Refrigerating the meatball mixture for 30 minutes before shaping helps retain the flavors and firm texture.
Preheat your oven to 250°F. Roll the mixture into balls about an inch in diameter; this size is perfect for even cooking and serving.
Place the meatballs on a baking sheet lined with parchment paper, ensuring they don’t touch. Bake for about 25 minutes; this step firms up the meatballs while keeping them tender.
While the meatballs are in the oven, heat olive oil in a large saucepan over medium heat. Sauté onions until soft and golden, then add minced garlic and fresh chili.
Stir until fragrant. Pour in the tomato passata and season with salt. Lower the heat to a gentle simmer, and allow the sauce to reduce into a velvety texture, developing rich and aromatic flavors.
Nestle the baked meatballs into the saucepan, making sure they’re all coated in the sauce. Cover and simmer on low for 20 minutes. Gently stir occasionally to keep the meatballs from sticking to the bottom.
This slow cooking method lets the flavors meld beautifully, making each bite even more irresistible.