Finely chop the onions. Crush or finely chop the garlic. Finely chop the parsley leaves, discarding the stems. Pick the oregano leaves, discarding the stems. Finely grate the parmesan.
Step 2 — Cook onion and garlic
Heat 20g butter in a medium saucepan over medium-high heat. Cook the onion and garlic, stirring occasionally, for 3-4 mins until softened. Transfer half the onion mixture to a large heatproof bowl and set aside to cool slightly.
Step 3 — Cook tomato sugo
Add half the tomato paste*, 10g butter and 2 tsp sugar to the onion mixture in the pan. Cook over medium heat, stirring, for 2 mins or until slightly darkened. Add the canned and fresh tomatoes and season with salt. Cook, covered, stirring occasionally, for 20 mins or until saucy. Stir in 2 tsp red wine vinegar. Taste, then season with salt and pepper.
Step 4 — Make meatballs
While the tomato sugo is cooking, bring a medium saucepan of salted water to the boil for the spaghetti. Add the beef mince, breadcrumbs, parsley, half the parmesan, a small pinch of chilli flakes* (omit the chilli if preferred) and 1 egg to the cooled onion mixture. Season with salt and pepper. Using damp hands, combine well, then shape into walnut-sized balls.
Step 5 — Cook meatballs and sugo
Heat 1 tsp olive oil in a medium frypan over medium-high heat. Cook the meatballs, turning regularly, for 4-5 mins until browned (the meatballs won't be cooked through). Add the tomato sugo to the meatballs and reduce the heat to low. Cook, covered, stirring occasionally, for 15 mins or until the meatballs are cooked through.
Step 6 — Cook spaghetti and serve
Meanwhile, add the spaghetti to the pan of boiling water. Cook, stirring occasionally, for 12 mins or until al dente. Drain. Add 10g butter to the spaghetti and toss to coat. Divide the spaghetti and meatball sugo among bowls. Drizzle over the pesto and scatter with the oregano and remaining parmesan to serve.