Onions: 2 large, thinly sliced
Spaghetti: 350g
Butter: 40g
Olive oil: 2 tbsp
Garlic: 2 cloves, finely sliced
Chilli flakes: 1 tsp (optional, for gentle heat)
Sea salt and freshly ground black pepper: to taste
Fresh flat-leaf parsley: small handful, finely chopped
Parmesan cheese: 50g, grated (optional, for serving)Method
Bring a large pan of salted water to the boil and cook the spaghetti until al dente. Before draining, save a cupful of the pasta water. While the pasta cooks, heat the olive oil and butter in a large frying pan over medium heat. Add the sliced onions and gently cook for 20–25 minutes, stirring often, until beautifully soft and caramelised. Stir in the garlic and cook for a further 1–2 minutes until fragrant. Add the chilli flakes if using, and season with salt and pepper to taste. Toss the drained pasta through the onions, adding a splash of reserved pasta water to help everything come together into a glossy, silky sauce. Finish with a scatter of chopped parsley and serve immediately.