Place the fresh breadcrumbs in a small bowl and pour the whole milk over them. Use a fork to combine, then set aside for 5 minutes to allow the bread to fully absorb the milk. It should form a soft, paste-like mixture.
In a large mixing bowl, combine the ground beef, ground pork, and ground veal.
Add the soaked breadcrumb mixture, beaten eggs, Parmesan, minced garlic, parsley, dried oregano, salt, and pepper.
Using clean hands, mix gently until just combined. Do not overmix work the mixture only until the ingredients are distributed evenly. Overworking develops the proteins and results in a dense, tough meatball.
Using a cookie scoop or your hands, portion the mixture into balls approximately 4–5 cm (1.5–2 inches) in diameter. Roll gently between your palms to smooth. You should get approximately 18–20 meatballs.
Place on a parchment-lined baking sheet and refrigerate for 15 minutes if time allows this helps them hold their shape during browning.
Heat 3 tablespoons of olive oil in a large heavy skillet over medium-high heat.
Working in batches, add the meatballs in a single layer without crowding. Brown on all sides, turning carefully with tongs, approximately 3–4 minutes per batch. They do not need to be cooked through at this stage you are building a crust and developing colour.
Transfer browned meatballs to a plate. Repeat with remaining meatballs.
In a large saucepan or Dutch oven, heat 2 tablespoons of olive oil over medium heat.
Add the diced onion and cook, stirring occasionally, for 8–10 minutes until soft and translucent. Do not rush this step the onion sweetens and deepens as it cooks.
Add the garlic and cook for a further 1 minute until fragrant.
Pour in the crushed San Marzano tomatoes. Add the salt, pepper, dried oregano, and sugar if using. Stir to combine.
Bring the sauce to a gentle simmer, then taste and adjust seasoning.
Carefully nestle all browned meatballs into the sauce. Spoon the sauce over them gently.
Reduce the heat to low, partially cover the pan, and simmer for 25–30 minutes, turning the meatballs once halfway through. The sauce will thicken and the meatballs will finish cooking through.
Remove from heat and stir in the torn fresh basil.
Serve immediately, or rest for 10 minutes the flavour continues to develop as it sits.