1. Cook the pasta in plenty of boiling salted water according to the instructions on the package.
2. Melt the butter in a large saucepan and fry the onion for 10 minutes until softened.
3. Stir in the garlic, fresh thyme, spinach and seasoning and heat gently for about 5 minutes, stirring occasionally, until heat through.
4. Stir in the mascarpone cheese and cook gently until heated through. Do not boil.
5. Drain the pasta thoroughly and stir into the sauce. Toss until well coated. Serve immediately. You can garnished with fresh thyme.
Hint: Mascarpone is a rich Italian cream cheese. If you cannot find any, use ordinary full-fat cream cheese instead.
Serves 4.