Prepare the breadcrumb mixture: In a small bowl, combine the breadcrumbs and milk. Stir gently and let the mixture sit for 5 minutes. The breadcrumbs will absorb the milk and turn into a soft, thick paste — this is the key to tender meatballs that do not dry out during the long cooking time.

Mix the meatball base: In a large mixing bowl, place the beef mince, beaten egg, soaked breadcrumbs, grated onion, minced garlic, Parmesan, parsley, oregano, salt, and pepper. Use your hands to combine everything gently — the mixture should feel cool, slightly sticky, and uniformly blended. Be careful not to overwork the meat, or the meatballs will become dense and tough.

Shape the meatballs: With slightly damp hands, roll the mixture into golf ball-sized portions, about 4 to 5 centimetres in diameter. You should get roughly 20 to 24 meatballs. Place them on a baking tray lined with baking parchment as you go. The surface of each meatball should feel smooth and even, with no cracks.

Brown the meatballs (optional but recommended): Heat the olive oil in a large frying pan over a medium-high heat. Working in two batches to avoid crowding the pan, add the meatballs and cook for 3 to 4 minutes, turning occasionally, until they are browned on all sides. You will hear a satisfying sizzle as they hit the pan, and the surfaces will turn a deep, rich brown. This step adds a layer of savoury flavour to the final dish, but if you are truly pressed for time, you can skip it and add the raw meatballs directly to the slow cooker.

Prepare the marinara sauce: In a medium bowl, stir together the tinned chopped tomatoes, tomato purée, and sugar. The sauce will look a little thin at this stage, but do not worry — it will thicken and concentrate as it simmers in the slow cooker.

Assemble in the slow cooker: Pour half of the tomato sauce into the bottom of the slow cooker insert. Arrange the browned (or raw) meatballs in a single layer on top of the sauce. Pour the remaining sauce over the meatballs, ensuring each one is mostly covered. The meatballs should be nestled snugly in the sauce, with the liquid reaching about halfway up their sides.

Cook low and slow: Place the lid on the slow cooker and cook on low for 4 to 5 hours. After 3 hours, the kitchen will begin to smell intensely of tomatoes and herbs, and the sauce will have darkened to a deep brick-red colour. The meatballs will be tender enough to break apart with a fork, and the sauce will have thickened to a silky, clingy consistency. Do not lift the lid during the first 3 hours of cooking, as each peek releases valuable heat and extends the cooking time.

Finish and serve: Once the meatballs are cooked through and tender, taste the sauce and adjust the seasoning with a little extra salt or pepper if needed. Garnish with a scattering of fresh parsley before serving.