Put the basil, garlic, thyme, bay leaf and oil in a saucepan and cook for one minute. Stir in the wine and tomatoes. Bring to the boil and add the tomato puree. Reduce to low heat and cook for 30 minutes, stirring occasionally.
Melt the remaining butter and fry the green peppers and onion. Cook for 10 minutes, stirring. Add the mushrooms and cook for a further 5 minutes.
Pour the sauce into the pan and stir in the cornflour. Season to taste and cook for 3 more minutes, stirring all the time.
Meanwhile, bring a pan of salted water to the boil and cook the spaghetti for about 10 minutes until ‘al dente’.
Drain and transfer to a warm dish. Toss in half the butter.
Discard the bay leaf from the sauce and pour over the spaghetti. Garnish with parsley, and serve at once.