Heat 15 ml of olive oil in a large, heavy-based casserole or saucepan over a medium-high heat until it shimmers.
Add 450 g lean beef mince, break it up with a wooden spoon and cook for 6–8 minutes until browned with no pink remaining. Drain off any excess fat, leaving a little for flavour.
Reduce the heat to medium and stir in the chopped brown onion. Cook for 5–7 minutes until softened and translucent.
Stir in the minced garlic and cook for about 1 minute until fragrant, taking care not to let it burn.
Push the meat and onion mixture to one side of the pan. Add 2 tbsp tomato purée and cook for 2–3 minutes, stirring occasionally, until it darkens and begins to caramelise.
Stir in 4 tins chopped tomatoes (400 g each), 250 ml beef stock, 1 tsp dried oregano, 1 tsp dried basil and 1 bay leaf. Season with 1 tsp caster sugar, 1 tsp salt and ½ tsp freshly ground black pepper, then stir to combine.
Bring to a gentle simmer, reduce the heat to low, cover and cook for 1–2 hours, stirring occasionally, until the sauce has thickened and the colour deepened.
Remove and discard the bay leaf. Taste and adjust the seasoning with extra salt and pepper if needed.
Serve the sauce over cooked spaghetti or penne and sprinkle over grated Parmesan to serve.