Fill a large saucepan with water, add a pinch of salt and bring to the boil.
Add the cavatappi to the pan and cook for 9–11 minutes until al dente. Before draining, scoop out about 250ml of the cooking water, then drain the pasta.
Heat the olive oil in a large frying pan over medium–high heat. Add the sausage meat, breaking it up with a spoon, and fry for 6–8 minutes until browned all over. Drain off any excess fat, leaving about 1 tbsp in the pan, then transfer the sausage meat to a plate.
Turn the heat down to medium, add the chopped brown onion and cook for 5–7 minutes until softened and translucent.
Add the garlic and cook for 1 minute, until fragrant.
Pour in the chopped tomatoes and chicken stock, stir well and bring to a gentle simmer. Reduce the heat to low, cover and simmer for 10 minutes.
Uncover and stir in the double cream, grated Parmesan, salt and freshly ground black pepper. Cook for 2–3 minutes, stirring occasionally, until the sauce is smooth and creamy.
Add the cooked cavatappi to the sauce and toss to coat. If it seems too thick, stir in a little of the reserved cooking water until you reach the desired consistency.
Stir through the chopped basil, then serve immediately, sprinkled with extra Parmesan.